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Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2017	Feb. 09, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	SPSC
Entity Registrant Name	SPS COMMERCE INC
Entity Central Index Key	0001092699
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		17,250,664
Entity Public Float			$ 1.1

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
CURRENT ASSETS
Cash and cash equivalents	$ 123,127	$ 115,877
Short-term investments	40,192	23,076
Accounts receivable, net	24,897	20,746
Deferred costs	25,091	19,224
Other current assets	6,149	7,010
Total current assets	219,456	185,933
PROPERTY AND EQUIPMENT, net	16,856	15,314
GOODWILL	51,613	49,777
INTANGIBLE ASSETS, net	16,529	19,788
INVESTMENTS	5,206	7,494
OTHER ASSETS
Deferred costs	6,770	6,086
Deferred income tax asset	17,551	12,446
Other assets	1,539	1,527
Total assets	335,520	298,365
CURRENT LIABILITIES
Accounts payable	4,463	2,302
Accrued compensation	15,886	13,740
Accrued expenses	4,712	3,508
Deferred revenue	16,407	11,055
Deferred rent	1,679	1,556
Total current liabilities	43,147	32,161
OTHER LIABILITIES
Deferred revenue	10,602	10,847
Deferred rent	3,064	4,179
Deferred income tax liability	1,887	1,911
Total liabilities	58,700	49,098
COMMITMENTS and CONTINGENCIES
STOCKHOLDERS’ EQUITY
Preferred stock, $0.001 par value; 5,000,000 shares authorized; 0 shares issued and outstanding
Common stock, $0.001 par value; 55,000,000 shares authorized; 17,249,153 and 17,081,145 shares issued; and 17,127,006 and 17,081,145 outstanding, respectively	17	17
Treasury stock, at cost; 122,147 and 0 shares, respectively	(5,815)
Additional paid-in capital	301,863	286,315
Accumulated deficit	(19,902)	(33,739)
Accumulated other comprehensive income (loss)	657	(3,326)
Total stockholders’ equity	276,820	249,267
Total liabilities and stockholders’ equity	$ 335,520	$ 298,365

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	55,000,000	55,000,000
Common stock, shares issued	17,249,153	17,081,145
Common stock, shares outstanding	17,127,006	17,081,145
Treasury stock, shares	122,147	0

Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenues	$ 220,566	$ 193,295	$ 158,518
Cost of revenues	73,625	64,346	50,043
Gross profit	146,941	128,949	108,475
Operating expenses
Sales and marketing	73,295	65,886	55,374
Research and development	23,183	21,981	17,954
General and administrative	37,461	28,827	24,817
Amortization of intangible assets	4,574	4,738	3,307
Total operating expenses	138,513	121,432	101,452
Income from operations	8,428	7,517	7,023
Other income (expense)
Interest income, net	1,032	601	197
Other income (expense), net	(320)	732	(145)
Total other income, net	712	1,333	52
Income before income taxes	9,140	8,850	7,075
Income tax expense	11,580	3,140	2,436
Net (loss) income	$ (2,440)	$ 5,710	$ 4,639
Net (loss) income per share
Basic	$ (0.14)	$ 0.34	$ 0.28
Diluted	$ (0.14)	$ 0.33	$ 0.27
Weighted average common shares used to compute net (loss) income per share
Basic	17,183	16,947	16,565
Diluted	17,183	17,241	17,032
Other comprehensive income
Foreign currency translation adjustments	$ 3,944	$ 336	$ (2,119)
Unrealized loss on investments, net of tax of $0, $5 and $31		(9)	(59)
Reclassification of unrealized loss on investments into earnings, net of tax of $24, $0 and $0	39
Comprehensive income	$ 1,543	$ 6,037	$ 2,461

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Unrealized loss on investments, tax	$ 0	$ 5	$ 31
Reclassification of unrealized loss on investments into earnings, tax	$ 24	$ 0	$ 0

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2014	$ 205,091	$ 16		$ 250,633	$ (44,088)	$ (1,470)
Beginning balance, shares at Dec. 31, 2014		16,348,747
Stock-based compensation	6,379			6,379
Exercise of stock options and issuance of restricted stock	4,440	$ 1		4,439
Exercise of stock options and issuance of restricted stock, shares		346,885
Excess tax benefit of stock options exercised	2,336			2,336
Employee stock purchase plan	1,478			1,478
Employee stock purchase plan, shares		28,362
Net income (loss)	4,639				4,639
Foreign currency translation adjustments	(2,119)					(2,119)
Unrealized loss on investments	(59)					(59)
Ending balance at Dec. 31, 2015	222,185	$ 17		265,265	(39,449)	(3,648)
Ending balance, shares at Dec. 31, 2015		16,723,994
Stock-based compensation	8,023			8,023
Exercise of stock options and issuance of restricted stock	4,303			4,303
Exercise of stock options and issuance of restricted stock, shares		279,841
Excess tax benefit of stock options exercised	4,070			4,070
Employee stock purchase plan	1,732			1,732
Employee stock purchase plan, shares		33,357
Stock issued for acquisition	2,922			2,922
Stock issued for acquisition, Shares		43,953
Net income (loss)	5,710				5,710
Foreign currency translation adjustments	336					336
Reclassification of losses on investments into earnings	18					18
Unrealized loss on investments	(32)					(32)
Ending balance at Dec. 31, 2016	249,267	$ 17		286,315	(33,739)	(3,326)
Ending balance, shares at Dec. 31, 2016		17,081,145
Stock-based compensation	12,728			12,728
Exercise of stock options and issuance of restricted stock	1,410			1,410
Exercise of stock options and issuance of restricted stock, shares		135,906
Cumulative-effect adjustment for previously unrecognized excess tax benefits	16,277				16,277
Employee stock purchase plan	1,933			1,933
Employee stock purchase plan, shares		40,968
Retirement of escrow shares	(523)			(523)
Retirement of escrow shares, shares		(8,866)
Repurchases of common stock	(5,815)		$ (5,815)
Repurchases of common stock, shares		(122,147)	122,147
Net income (loss)	(2,440)				(2,440)
Foreign currency translation adjustments	3,944					3,944
Reclassification of losses on investments into earnings	39					39
Ending balance at Dec. 31, 2017	$ 276,820	$ 17	$ (5,815)	$ 301,863	$ (19,902)	$ 657
Ending balance, shares at Dec. 31, 2017		17,127,006	122,147

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net (loss) income	$ (2,440)	$ 5,710	$ 4,639
Reconciliation of net (loss) income to net cash provided by operating activities
Deferred income taxes	10,854	(1,698)	(38)
Share-based earn-out liability		(1,103)
Depreciation and amortization of property and equipment	7,208	6,598	6,265
Amortization of intangible assets	4,574	4,738	3,307
Provision for doubtful accounts	1,705	1,375	1,271
Stock-based compensation	12,728	8,023	6,379
Other, net	(15)
Changes in assets and liabilities, net of effects of acquisition
Accounts receivable	(5,586)	(3,735)	(3,517)
Deferred costs	(6,548)	(4,964)	(3,023)
Other current and non-current assets	393	(1,911)	(2,037)
Accounts payable	832	(382)	(1,569)
Accrued compensation	2,073	2,180	1,295
Accrued expenses	1,192	990	(461)
Deferred revenue	5,107	2,710	587
Deferred rent	(1,027)	234	1,331
Net cash provided by operating activities	31,050	18,765	14,429
Cash flows from investing activities
Purchases of property and equipment	(7,271)	(8,008)	(8,757)
Purchases of investments	(47,878)	(23,135)	(22,527)
Maturities of investments	33,029	15,018
Acquisition of business and intangible assets, net of cash acquired	(500)	(18,032)
Net cash used in investing activities	(22,620)	(34,157)	(31,284)
Cash flows from financing activities
Repurchases of common stock	(5,815)
Net proceeds from exercise of options to purchase common stock	1,410	4,303	4,440
Excess tax benefit from exercise of options to purchase common stock		4,070	2,336
Net proceeds from employee stock purchase plan	1,933	1,732	1,478
Net cash (used in) provided by financing activities	(2,472)	10,105	8,254
Effect of foreign currency exchange rate changes	1,292	(374)	(656)
Net increase (decrease) in cash and cash equivalents	7,250	(5,661)	(9,257)
Cash and cash equivalents at beginning of year	115,877	121,538	130,795
Cash and cash equivalents at end of year	123,127	115,877	121,538
Supplemental disclosure of cash flow information
Cash paid for income taxes, net	1,068	722	$ 114
Non-cash financing activities:
Net purchases of property and equipment on account	$ 1,335
Common stock issued for business acquisitions		$ 2,922

General	12 Months Ended
General	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
General	NOTE A – General Business Description We are a leading provider of cloud-based supply chain management solutions, providing network-proven fulfillment, sourcing and item assortment management solutions, along with comprehensive retail performance analytics to thousands of customers worldwide. We provide our solutions through the SPS Commerce Platform, a cloud-based product suite that improves the way retailers, suppliers, distributors and logistics firms orchestrate the sourcing, set up of new vendors and items, and fulfillment of the products that consumers buy. We derive the majority of our revenues from thousands of monthly recurring subscriptions from businesses that utilize our solutions. Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of SPS Commerce, Inc. and its subsidiaries. All intercompany accounts and transactions have been eliminated in the consolidated financial statements. Foreign Currency Translation Assets and liabilities denominated in currencies other than the U.S. dollar are translated into U.S. dollars at the exchange rates in effect at the balance sheet date, with the resulting translation adjustments recorded as a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at the average exchange rates during the year. Foreign currency transaction gains and losses, if any, are included in net income (loss). Use of Estimates Preparing financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. Business Combinations We recognize separately from goodwill the fair value of the assets acquired and the liabilities assumed at the acquisition date. Goodwill as of the acquisition date is measured as the excess of consideration transferred and the net of the acquisition date amounts of the assets acquired and the liabilities assumed. Assets acquired include tangible and intangible assets. We use estimates and assumptions that we believe are reasonable as a part of determining the value and useful lives of purchased intangible assets and the purchase price allocation process. While we believe these estimates and assumptions are reasonable, they are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, we may record adjustments to the fair value of the assets acquired and the liabilities assumed. Any such adjustments would be recorded as an offset to goodwill. Upon the conclusion of the measurement period or final determination of the fair values, whichever comes first, any subsequent adjustments would be recorded in our consolidated statements of comprehensive income. Segment Information We operate in and report on one segment, which is supply chain management solutions. Risk and Uncertainties We rely on hardware and software licensed from third parties to offer our on-demand solutions. Our management believes alternate sources are available; however, disruption or termination of these relationships could adversely affect our operating results in the near term. Concentration of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist principally of temporary cash and cash equivalents in financial institutions in excess of federally insured limits and trade accounts receivable. Temporary cash investments are held with financial institutions that we believe are subject to minimal risk. Cash and Cash Equivalents Cash and cash equivalents consist of cash and highly liquid investments with original maturities of less than 90 days. Cash and cash equivalents are stated at fair value. Investments Management determines the appropriate classification of certificates of deposit and marketable securities at the time of purchase and reevaluates such determination at each balance sheet date. Securities are classified as available for sale and are carried at fair value, with the change in unrealized gains and losses, net of tax, reported as a separate component on the consolidated statements of comprehensive income. Fair value is determined based on quoted market rates when observable or utilizing data points that are observable, such as quoted prices, interest rates and yield curves. When a determination has been made that an other-than-temporary decline in fair value has occurred, the amount of the decline that is related to a credit loss is realized and is included in other income (expense), net in the consolidated statements of comprehensive income. Fair Value of Financial Instruments The carrying amounts of our financial instruments, which include cash, cash equivalents, accounts receivable, accounts payable and other accrued expenses, approximates fair value due to their short maturities. Marketable securities are recorded at fair value as further described in Note C. Accounts Receivable Accounts receivable are initially recorded upon the sale of solutions to customers. Credit is granted in the normal course of business without collateral. Accounts receivable are stated net of allowances for doubtful accounts, which represent estimated losses resulting from the inability of certain customers to make the required payments. When determining the allowances for doubtful accounts, we take several factors into consideration including the overall composition of the accounts receivable aging, our prior history of accounts receivable write-offs, the type of customers and our experience with specific customers. We write-off accounts receivable when they are determined to be uncollectible. Changes in the allowances for doubtful accounts are recorded as bad debt expense and are included in general and administrative expense in our consolidated statements of comprehensive income. Property and Equipment Property and equipment, including assets acquired under capital lease obligations, are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives when placed in service, which are: Computer equipment and software: 2 to 3 years Office equipment and furniture: 5 to 7 years Leasehold improvements: the shorter of the useful life of the asset or the remaining term of the lease Significant additions or improvements extending asset lives beyond one year are capitalized, while repairs and maintenance are charged to expense as incurred. We also capitalize and amortize eligible costs to acquire or develop internal-use software that are incurred during the development stage. The assets and related accumulated depreciation and amortization are adjusted for asset retirements and disposals with the resulting gain or loss included in our consolidated statements of comprehensive income. Research and Development Research and development costs primarily include maintenance and data conversion activities related to our cloud-based supply chain management solutions and are expensed as incurred. Goodwill Goodwill represents the excess of the purchase price over the fair value of identifiable net assets acquired in business combinations. We test goodwill for impairment annually at November 30, or more frequently if events or changes in circumstances indicate that the asset might be impaired. The impairment test is conducted by comparing the fair value of the net assets with the carrying value of the reporting unit. Fair value is determined using the direct market observation of market price and outstanding equity of the reporting unit at the testing date. If the carrying value of the goodwill exceeds the fair value of the reporting unit, goodwill may be impaired. If this occurs, the fair value is then allocated to its assets and liabilities in a manner similar to a purchase price allocation in order to determine the implied fair value of goodwill. This implied fair value is then compared to the carrying amount of goodwill and, if it is less, we would recognize an impairment loss. Intangible Assets Assets acquired in business combinations may include identifiable intangible assets such as subscriber relationships and non-competition agreements. We recognize separately from goodwill the fair value of the identifiable intangible assets acquired. We have determined the fair value and useful lives of our purchased intangible assets using certain estimates and assumptions that we believe are reasonable. The purchased intangible assets are being amortized on a straight-line basis over their estimated useful lives, which are three to nine years for subscriber relationships, two to five years for non-competition agreements and one to four years for technology and other. Impairment of Long-Lived Assets We review our long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. The carrying amount of a long-lived asset is not recoverable if the carrying amount of an asset group exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the assets at the date it is tested for recoverability, whether in use or under development. An impairment loss is measured as the amount by which the carrying amount of a long-lived asset exceeds its fair value. Revenue Recognition We generate revenues by providing three types of solutions to our customers; fulfillment, enablement and analytics. Our cloud-based solutions allow our customers to meet their supply chain management requirements. Revenues are recognized when all of the following criteria are met: (1) persuasive evidence of an arrangement exists, (2) delivery has occurred, (3) the fee is fixed or determinable, and (4) collectability is probable. If collection is not considered probable, revenues are recognized when the fees are collected. Fees related to our fulfillment and analytics solutions consist of two revenue sources: set-up fees and recurring monthly fees. Set-up fees are specific for each connection a customer has with a trading partner and most of our customers have connections with numerous trading partners. Set-up fees are nonrefundable upfront fees that do not have standalone value to our customer and are not separable from the recurring monthly fees. All set-up fees and related costs are deferred and recognized ratably over the average life of the connection between the customer and the trading partner, which is approximately two years. We begin recognizing set-up fee revenue once the connection is established. Set-up fees for which connections have not yet been established are classified as long-term. We continue to evaluate the length of the amortization period as more experience is gained with cancellations and technology changes requested by our customers. It is possible that, in the future, the period over which such subscription set-up fees and costs are amortized may be adjusted. Any change in our estimate of the average connection life will affect our future results of operations. The recurring monthly fees are comprised of both fixed and transaction-based fees that are recognized as earned. Stock-Based Compensation We recognize the cost of all share-based payments to employees, including grants of employee stock options, in the financial statements based on the grant date fair value of those awards. This cost is recognized over the period for which an employee is required to provide service in exchange for the award. We estimate the fair value of options granted using the Black-Scholes option pricing model. In valuing share-based awards, judgment is required in determining the expected volatility of common stock and the expected term individuals will hold their share-based awards prior to exercising. The expected volatility of the options is based on the historical volatility of our common stock. The expected term of the options is based on the simplified method which does not consider historical employee exercise behavior. Income Taxes We account for income taxes using the liability method, which requires recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance when, in our judgement, there is a less than a 50% likelihood that the deferred tax asset will be utilized. We assess our ability to realize our deferred tax assets at the end of each reporting period. Realization of our deferred tax assets is contingent upon future taxable earnings. Accordingly, this assessment requires significant estimates and judgment. If the estimates of future taxable income vary from actual results, our assessment regarding the realization of these deferred tax assets could change. Future changes in the estimated amount of deferred taxes expected to be realized will be reflected in our consolidated financial statements in the period the estimate is changed, with a corresponding adjustment to our operating results. We recognize the financial statement benefit of a tax position only after determining that the relevant tax authority would “more likely than not” sustain the position following an audit. For tax positions meeting the “more likely than not” threshold, the amount recognized in the financial statements is the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement with the relevant tax authority. Net Income (Loss) Per Share Basic net income (loss) per share has been computed using the weighted average number of shares of common stock outstanding during each period. Diluted net income (loss) per share also includes the impact of our outstanding potential common shares, including options, restricted stock units and restricted stock awards. Potential common shares that are anti-dilutive are excluded from the calculation of diluted net income (loss) per share. Recently Adopted Accounting Pronouncements In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”). The new guidance requires excess tax benefits and tax deficiencies to be recorded in the income statement when the awards vest or are settled and provides an accounting policy election to account for forfeitures as they occur. In addition, cash flows related to excess tax benefits will no longer be separately classified as a financing activity apart from other income tax cash flows within operating activities. The standard also allows entities to repurchase more of an employee’s shares for tax withholding purposes without triggering liability accounting and clarifies that all cash payments made on an employee’s behalf for withheld shares should be presented as a financing activity on the statements of cash flows. The standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, with early adoption permitted. We adopted ASU 2016-09 during the year ended December 31, 2017. The impact to our consolidated balance sheet as of January 1, 2017 was a $16.3 million increase in deferred income tax assets and a corresponding $16.3 million decrease in accumulated deficit. This impact results from the cumulative-effect adjustment for previously unrecognized excess tax benefits using the modified retrospective method required by the new standard. We elected to adopt the changes in cash flow statement presentation prospectively to be consistent with the prospective transition for the treatment of excess tax benefits in the income statement. Accordingly, we no longer classify excess tax benefits as a financing activity subsequent to January 1, 2017. On December 22, 2017, the Securities and Exchange Commission (“SEC”) staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP related to the enactment of the comprehensive tax legislation, commonly referred to as the Tax Cut and Jobs Act (“Tax Act”). This guidance was adopted in the fourth quarter of 2017. Additional information regarding our adoption of this guidance is contained in Note J. Recent Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance will replace most existing revenue recognition guidance in GAAP when it becomes effective. These new requirements are effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual periods. The new revenue recognition standard will not materially impact our recognition of the primary fees received from customers for our cloud-based supply chain solutions. The adoption of the new standard will impact our accounting for certain upfront set-up fees and the periods over which the related revenues are recognized, as well as the timing of cost recognition for some sales commissions. When compared to previously reported amounts, revenue will decrease $0.5 million and $0.1 million for the years ended December 31, 2017 and 2016, respectively. Commission expense, which is reported in sales and marketing expense, will decrease $2.0 million for the year ended December 31, 2017 and increase $1.0 million for the year ended December 31, 2016. In February 2016, the FASB issued ASU 2016-02, Leases, which will supersede existing lease guidance and will require all leases with a term greater than 12 months to be recognized in the statements of financial position and eliminate current real estate-specific lease guidance, while maintaining substantially similar classification criteria for distinguishing between finance leases and operating leases. This standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. We believe the adoption of the new lease accounting standard will materially impact our consolidated financial statements by increasing our non-current assets and non-current liabilities on our consolidated balance sheets in order to record the right of use assets and related lease liabilities for our existing operating leases. We are in the process of determining the financial statement impact and are currently unable to estimate the impact on our consolidated financial statements. In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), which simplifies the test for goodwill impairment by eliminating step two from the goodwill impairment test. Under the new guidance, an entity should recognize an impairment charge for the amount based on the excess of a reporting unit’s carrying amount over its fair value. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. This guidance is effective for annual and interim impairment tests performed in periods beginning after December 15, 2019 on a prospective basis, and earlier adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. We believe the adoption of this standard will not have a material impact on our consolidated financial statements.

Business Acquisitions

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Business Acquisitions

NOTE B – Business Acquisitions

Toolbox Solutions, Inc.

On January 5, 2016, we completed our acquisition of all of the outstanding common shares of Toolbox Solutions, Inc. (“Toolbox Solutions”), a privately held company providing point-of-sale analytics and category management services to retailers and consumer packaged goods suppliers in North America. This acquisition expanded our retail network and strengthened our analytics offerings. Pursuant to the share purchase agreement, we paid $18.0 million in cash and issued $2.9 million in stock, or 43,953 shares of common stock, to the shareholders of Toolbox Solutions. The purchase agreement also allowed the sellers to receive up to 16,222 additional shares of common stock, which would have become payable contingent upon the completion of certain revenue milestones, none of which were met, and therefore, no additional shares were issued. During the year ended December 31, 2016, we recognized other income of $1.1 million in our consolidated statements of comprehensive income due to the remeasurement of this contingent liability.

Purchase Price Allocation

We accounted for the acquisition as a business combination. We allocated the purchase price to the tangible and identifiable intangible assets acquired and liabilities assumed based on their estimated fair values as of the acquisition date. We engaged a third-party valuation firm to assist us in the determination of the value of the purchased intangible assets. The excess of the purchase price over the fair value of net tangible and identifiable intangible assets acquired was recorded as goodwill. Goodwill is attributed to a trained workforce and other buyer-specific value resulting from expected synergies, including long-term cost savings, which are not included in the fair values of identifiable assets.

The purchase price consisted of the following (in thousands):

Cash	$	18,032
SPS Commerce, Inc. common stock		2,922
Fair value of share-based earn-out liability		1,043
	$	21,997

The final purchase price was subject to a net working capital adjustment to be determined by the sellers and us, pursuant to the terms of the purchase agreement. The number of shares of our common stock issued for the acquisition was a net of 43,953 shares, which consisted of 48,668 shares issued at closing, as calculated according to the terms of the purchase agreement, less 4,715 shares that were returned to us from escrow in the fourth quarter of 2016.

The following table summarizes the estimated fair values of the assets acquired, net of cash acquired of $0.4 million, and liabilities assumed at the acquisition date (in thousands):

Current assets	$	1,253
Property and equipment		56
Goodwill		15,389
Intangible assets		9,070
Current liabilities		(1,249	)
Deferred revenue		(301	)
Deferred income tax liability		(2,221	)
	$	21,997

Purchased Intangible Assets

The following table summarizes the estimated fair value of the purchased intangible assets and their estimated useful lives:

	Estimated		Estimated
	Fair Value		Life
Purchased Intangible Assets	(in thousands)		(in years)
Subscriber relationships	$	7,400		8
Developed technology		1,200		4
Trade names		70		1
Non-competition agreements		400		5
Total	$	9,070

The purchased intangible assets are being amortized on a straight-line basis over their estimated useful lives. Amortization expense for the period from January 5, 2016 through December 31, 2016 was $1.4 million.

Acquisition-Related Costs and Post-Acquisition Operating Results

Acquisition-related costs were $0.1 million and are included in our consolidated statement of comprehensive income for the year ended December 31, 2016. The operating results of Toolbox Solutions have been included in our consolidated financial statements since January 5, 2016, the closing date of the acquisition. For the period from January 5, 2016 through December 31, 2016, approximately $7.9 million of our revenues were derived from Toolbox Solutions’ products and services. The amount of operating income or loss from Toolbox Solutions was not separately identifiable due to our integration.

Unaudited Pro Forma Financial Information

The unaudited pro forma financial information in the table below presents the combined operating results of SPS Commerce and Toolbox Solutions as if the acquisition had occurred on January 1, 2015. The unaudited pro forma information includes the historical operating results of each company and pro forma adjustments for the approximately $1.4 million of annual amortization expense related to purchased intangible assets and the additional impact on the provision or benefit for income taxes, resulting from the combined income and intangible amortization expense, using our statutory blended income tax rate of 26.5%.

The unaudited pro forma financial information is presented for informational purposes only and is not necessarily indicative of the results of operations that would have actually been reported had the acquisition occurred on January 1, 2015, nor is it necessarily indicative of our results of operations for any future periods.

	Year Ended December 31,
(in thousands, except per share data)	2016		2015
Pro forma total revenue	$	193,525	$	166,873
Pro forma net income		5,976		2,400
Pro forma net income per share
Basic		0.35		0.14
Diluted		0.35		0.14

Financial Instruments

12 Months Ended

Dec. 31, 2017

Financial Instruments Owned At Fair Value [Abstract]

Financial Instruments

NOTE C – Financial Instruments

We invest primarily in money market funds, certificates of deposit, highly liquid debt instruments of the U.S. government and U.S. corporate debt securities. All highly liquid investments with original maturities of 90 days or less are classified as cash equivalents. All investments with original maturities greater than 90 days and remaining maturities less than one year from the balance sheet date are classified as short-term investments. Investments with remaining maturities of more than one year from the balance sheet date are classified as long-term investments.

Our short- and long-term marketable securities are classified as available-for-sale. We intend to hold marketable securities until maturity; however, we may sell these securities at any time for use in current operations or for other purposes. Consequently, we may or may not keep securities with stated holding periods to maturity.

Our marketable securities are carried at fair value and unrealized gains and losses on these investments, net of taxes, are included in accumulated other comprehensive loss in the consolidated balance sheets. Realized gains or losses are included in other income (expense), net in the consolidated statements of comprehensive income. When a determination has been made that an other-than-temporary decline in fair value has occurred, the amount of the decline that is related to a credit loss is realized and is included in other income (expense), net in the consolidated statements of comprehensive income.

Cash equivalents and short- and long-term investments consisted of the following (in thousands):

	December 31,
	2017							2016
	Amortized		Unrealized			Fair		Amortized		Unrealized			Fair
	Cost		Gains (Losses)			Value		Cost		Gains (Losses)			Value
Cash equivalents:
Money market funds	$	104,544	$	—		$	104,544	$	75,375	$	—		$	75,375
Certificate of deposit		7,814		—			7,814		—		—			—
Marketable securities:
Corporate bonds		17,758		(57	)		17,701		15,681		(96	)		15,585
Commercial paper		7,456		20			7,476		4,977		10			4,987
U.S. treasury securities		12,381		26			12,407		7,489		10			7,499
U.S. agency obligations		—		—			—		2,497		3			2,500
	$	149,953	$	(11	)	$	149,942	$	106,019	$	(73	)	$	105,946
Due within one year						$	144,736						$	98,452
Due within two years							5,206							7,494
Total						$	149,942						$	105,946

We do not believe any of the unrealized losses represent an other-than-temporary impairment based on our assessment of available evidence as of December 31, 2017. We expect to receive the full principal and interest on all of these cash equivalents and short- and long-term investments.

Fair Value Measurements

We measure certain financial assets at fair value on a recurring basis based on a fair value hierarchy that requires us to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. A financial instrument’s categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The three levels of inputs that may be used to measure fair value are:

•

Level 1 – quoted prices in active markets for identical assets or liabilities.

•

Level 2 – observable inputs other than Level 1 prices, such as (a) quoted prices for similar assets or liabilities, (b) quoted prices in markets with insufficient volume or infrequent transactions (less active markets), or (c) model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. We obtain the fair values of our level 2 available-for-sale securities from a professional pricing service.

•

Level 3 – unobservable inputs to the valuation methodology that are significant to the measurement of fair value of assets or liabilities.

The following table presents information about our financial assets that are measured at fair value on a recurring basis and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value (in thousands):

	Level 1		Level 2		Level 3		Total
Assets at December 31, 2017:
Cash equivalents:
Money market funds	$	104,544	$	—	$	—	$	104,544
Certificate of deposit		7,814		—		—		7,814
Marketable securities:
Corporate bonds		—		17,700		—		17,700
Commerical paper		—		7,477		—		7,477
U.S. treasury securities		—		12,407		—		12,407
	$	112,358	$	37,584	$	—	$	149,942
Assets at December 31, 2016:
Cash equivalents:
Money market funds	$	75,375	$	—	$	—	$	75,375
Marketable securities:
Corporate bonds		—		15,585		—		15,585
Commerical paper		—		4,987		—		4,987
U.S. treasury securities		—		7,499		—		7,499
U.S. agency obligations		—		2,500		—		2,500
	$	75,375	$	30,571	$	—	$	105,946

Allowance for Doubtful Accounts

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

Allowance for Doubtful Accounts

NOTE D – Allowance for Doubtful Accounts

The allowance for doubtful accounts activity, included in accounts receivable, net, was as follows (in thousands):

	2017			2016			2015
Balances, January 1	$	515		$	446		$	279
Provision for doubtful accounts		1,705			1,375			1,271
Write-offs, net of recoveries		(1,457	)		(1,306	)		(1,104	)
Balances, December 31	$	763		$	515		$	446

Property and Equipment, net

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment, net

NOTE E – Property and Equipment, net

Property and equipment, net included the following (in thousands):

	December 31,
	2017			2016
Computer equipment and software	$	35,326		$	29,270
Office equipment and furniture		7,439			7,087
Leasehold improvements		8,042			7,844
		50,807			44,201
Less: accumulated depreciation and amortization		(33,951	)		(28,887	)
	$	16,856		$	15,314

At December 31, 2017 and 2016, property and equipment, net included approximately $2.2 million and $2.1 million, respectively, of assets held at subsidiary and office locations outside of the U.S.

Goodwill and Intangible Assets, net

12 Months Ended

Dec. 31, 2017

Goodwill And Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets, net

NOTE F – Goodwill and Intangible Assets, net

The changes in the net carrying amount of goodwill for the years ended December 31, 2017 and 2016 are as follows (in thousands):

	2017		2016
Balances, January 1	$	49,777	$	33,848
Additions from business acquisitions		—		15,389
Foreign currency translation		1,836		540
Balances, December 31	$	51,613	$	49,777

Intangible assets, net included the following (in thousands):

	December 31, 2017
	Carrying Amount		Accumulated Amortization			Foreign Currency Translation		Net
Subscriber relationships	$	34,350	$	(19,592	)	$	614	$	15,372
Non-competition agreements		2,499		(2,058	)		45		486
Technology and other		2,130		(1,518	)		59		671
	$	38,979	$	(23,168	)	$	718	$	16,529

	December 31, 2016
	Carrying Amount		Accumulated Amortization			Foreign Currency Translation		Net
Subscriber relationships	$	33,736	$	(15,708	)	$	295	$	18,323
Non-competition agreements		2,234		(1,818	)		17		433
Technology and other		2,089		(1,120	)		63		1,032
	$	38,059	$	(18,646	)	$	375	$	19,788

Amortization expense was $4.6 million, $4.7 million and $3.3 million for the years ended December 31, 2017, 2016 and 2015, respectively. At December 31, 2017, future amortization expense for intangible assets was as follows (in thousands):

2018	$	4,022
2019		3,730
2020		3,365
2021		2,520
2022		1,449
Thereafter		1,443
	$	16,529

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

NOTE G – Commitments and Contingencies

Operating Leases

We are obligated under non-cancellable operating leases primarily for office space. Rent expense for all operating leases, which includes minimum lease payments and other charges such as common area maintenance fees, charged to operations was $4.9 million, $5.0 million and $4.6 million for the years ended December 31, 2017, 2016 and 2015, respectively.

On December 20, 2017, we executed the fourth amendment to our lease agreement for our current headquarters located in Minneapolis, Minnesota where we lease approximately 166,000 square feet under an agreement that expires on April 30, 2025. We have agreed to expand our headquarters premises by approximately 48,000 square feet during 2018 and 2020. Our lease agreement also includes a further expansion right and a right of first offer to lease certain additional space and two options to extend the term of the lease for five years at a market rate determined in accordance with the lease. We received $3.2 million in incentives upon execution of the amendment which have been incorporated into our deferred rent calculation.

At December 31, 2017, our future minimum payments under operating leases were as follows (in thousands):

2018	$	3,833
2019		3,847
2020		3,122
2021		3,624
2022		3,270
Thereafter		6,796
	$	24,492

Other Contingencies

We may be involved in various claims and legal actions in the normal course of business. Our management believes that the outcome of any such claims and legal actions will not have a material effect on our financial position, results of operations or cash flows.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2017
Equity [Abstract]
Stockholders’ Equity	NOTE H – Stockholders’ Equity Common Stock Issued In connection with the acquisition of Toolbox Solutions (see Note B), we issued a net of 43,953 shares which consisted of 48,668 shares issued at closing, as calculated according to the terms of the purchase agreement, less 4,715 shares that were returned to us from escrow in the fourth quarter of 2016. The fair value of the shares we issued, approximately $2.9 million, was determined using the closing price of our common stock on January 5, 2016. During the second quarter of 2017, 8,866 shares were returned from escrow pursuant to the agreement with Toolbox Solutions. Stock Repurchase Program On November 2, 2017, our board of directors authorized a program to repurchase up to $50.0 million of common stock. Under the program, purchases may be made from time to time in the open market over the next two years. The number of shares to be purchased and the timing of purchases will be based on the price of our common stock, general business and market conditions and other investment considerations and factors. The program does not obligate us to repurchase any specific number of shares and may be suspended or discontinued at any time without prior notice. We intend to finance the share repurchase program with cash on hand. During the fourth quarter of 2017, we repurchased 122,147 shares at a cost of $5.8 million. As of December 31, 2017, $44.2 million of the $50.0 million share repurchases authorized was available for future share repurchases.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

NOTE I – Stock-Based Compensation

Our equity compensation plans provide for the grant of incentive and nonqualified stock options, as well as other stock-based awards including restricted stock and restricted stock units, to employees, non-employee directors and other consultants who provide services to us. Restricted stock awards result in the issuance of new shares when granted. For other stock-based awards, new shares are issued when the award is exercised, vested or released according to the terms of the agreement. In February 2017 and February 2016, 1,024,868 and 1,003,439 additional shares, respectively, were reserved for future issuance under our 2010 Equity Incentive Plan. At December 31, 2017, there were approximately 4.6 million shares available for grant under approved equity compensation plans.

We recorded stock-based compensation expense of $12.7 million, $8.0 million and $6.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. During the year ended December 31, 2017, stock-based compensation expense included a $3.6 million charge due to immediate expensing of equity awards upon our Chief Executive Officer meeting certain age and years of service conditions. Stock-based compensation expense was allocated as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015
Cost of revenues	$	1,887	$	1,309	$	989
Operating expenses
Sales and marketing		2,197		2,412		1,978
Research and development		949		618		640
General and administrative		7,694		3,684		2,772
Total stock-based compensation expense	$	12,727	$	8,023	$	6,379

As of December 31, 2017, there was approximately $11.6 million of unrecognized stock-based compensation expense under our equity compensation plans, which is expected to be recognized on a straight-line basis over a weighted-average period of 2.5 years.

Stock Options

Stock options generally vest over four years and have a contractual term of seven to ten years from the date of grant. Our stock option activity was as follows:

				Weighted Average
	Options			Exercise Price
	(#)			($/share)
Outstanding at January 1, 2015		1,085,463		$	26.53
Granted		181,487			67.50
Exercised		(305,106	)		14.55
Forfeited		(18,741	)		45.82
Outstanding at December 31, 2015		943,103			37.91
Granted		340,609			48.58
Exercised		(221,630	)		19.42
Forfeited		(46,070	)		55.58
Outstanding at December 31, 2016		1,016,012			44.72
Granted		172,697			55.87
Exercised		(65,502	)		21.53
Forfeited		(25,876	)		55.93
Outstanding at December 31, 2017		1,097,331			47.60

Of the total outstanding options at December 31, 2017, 743,471 were exercisable with a weighted average exercise price of $44.58 per share. The total outstanding options had a weighted average remaining contractual life of 4.0 years.

The fair value of options that vested during the years ended December 31, 2017, 2016 and 2015 was $4.2 million, $3.4 million and $3.1 million, respectively.

The intrinsic value of options exercised during the years ended December 31, 2017, 2016 and 2015 was $2.8 million, $8.6 million and $16.8 million, respectively. The intrinsic value of outstanding options at December 31, 2017, 2016 and 2015 was $7.3 million, $25.6 million and $30.5 million, respectively.

The weighted-average fair values per share of options granted during the years ended December 31, 2017, 2016 and 2015 were $18.85, $16.13 and $23.09, respectively. The fair values of the options granted were estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2017			2016			2015
Volatility		38	%		38	%		39	%
Dividend yield		—			—			—
Life (in years)		4.51			4.54			4.52
Risk-free interest rate		1.85	%		1.19	%		1.36	%

The expected volatility of the options is based on the historical volatility of our common stock. We have not issued dividends on our common stock and do not expect to do so in the foreseeable future. The expected term of the options is based on the simplified method which does not consider historical employee exercise behavior. The risk-free interest rate is based on the U.S. Treasury rates at the date of grant with maturity dates approximately equal to the expected life at the grant date.

Performance Share Units and Restricted Stock Units and Awards

In February 2017, our executive officers were granted performance share unit (“PSU”) awards with vesting contingent on successful attainment of predetermined revenue targets over the course of a three-year performance period. No expense for PSU awards was recognized during the year ended December 31, 2017 as the probability of attainment of the revenue target decreased.

Restricted stock units (“RSU”) vest over four years and, upon vesting, the holder is entitled to receive shares of our common stock. With restricted stock awards (“RSA”), shares of our common stock are issued when the award is granted and the restrictions lapse over one year.

Our PSU and RSU activity was as follows:

				Weighted Average
	PSUs and RSUs			Grant Date Fair
	(#)			Value ($/share)
Outstanding at January 1, 2015		115,133		$	45.25
Granted		68,159			67.50
Vested and common stock issued		(37,669	)		40.91
Forfeited		(5,058	)		54.28
Outstanding at December 31, 2015		140,565			56.88
Granted		115,896			48.32
Vested and common stock issued		(52,133	)		48.19
Forfeited		(15,286	)		55.48
Outstanding at December 31, 2016		189,042			54.14
Granted		211,168			55.62
Vested and common stock issued		(64,950	)		53.64
Forfeited		(13,348	)		55.39
Outstanding at December 31, 2017		321,912			55.16

The number of PSUs and RSUs outstanding at December 31, 2017 included 44,177 units that have vested, but the shares of common stock have not yet been issued pursuant to the terms of the agreement.

Our RSA activity was as follows:

				Weighted Average
	RSAs			Grant Date Fair
	(#)			Value ($/share)
Outstanding at January 1, 2015		1,338		$	51.74
Restricted common stock issued		4,110			67.37
Restrictions lapsed		(4,416	)		62.63
Outstanding at December 31, 2015		1,032			67.39
Restricted common stock issued		6,078			52.27
Restrictions lapsed		(5,586	)		55.06
Outstanding at December 31, 2016		1,524			52.28
Restricted common stock issued		5,454			58.29
Restrictions lapsed		(5,610	)		56.65
Outstanding at December 31, 2017		1,368			58.29

Employee Stock Purchase Plan

Effective July 1, 2012, we adopted an employee stock purchase plan which allows participating employees to purchase shares of our common stock at a discount through payroll deductions. The plan is available to all employees subject to certain eligibility requirements. Participating employees may purchase common stock, on a voluntary after tax basis, at a price that is the lower of 85% of the fair market value of one share of common stock at the beginning or end of each stock purchase period. The plan consists of two six-month offering periods, beginning on January 1 and July 1 of each calendar year. A total of 1.0 million shares of common stock are remaining for issuance under the plan.

For the offering periods in 2017, 2016 and 2015, we withheld approximately $1.9 million, $1.7 million and $1.5 million, respectively, from employees participating in the plan and purchased 40,968 shares, 33,357 shares and 28,362 shares, respectively, on their behalf.

For the years ended December 31, 2017, 2016 and 2015, we recorded approximately $0.7 million, $0.6 million and $0.4 million, respectively, of stock-based compensation expense associated with the employee stock purchase plan. The fair value was estimated based on the market price of our common stock at the beginning of each offering period and using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2017			2016			2015
Volatility		32	%		37	%		30	%
Dividend yield		—			—			—
Life (in years)		0.50			0.50			0.50
Risk-free interest rate		0.90	%		0.42	%		0.12	%

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

NOTE J – Income Taxes

Our provisions for income taxes included current federal, foreign and state income tax expense, as well as deferred tax expense as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Current
Federal	$	(184	)	$	3,684		$	2,066
State		258			555			289
Foreign		652			599			119
Deferred
Federal		11,551			(988	)		103
State		(342	)		(133	)		(141	)
Foreign		(355	)		(577	)		—
	$	11,580		$	3,140		$	2,436

The current federal provision in the table above includes a $0.4 million reclass of alternative minimum tax (“AMT”) credit carryforwards from the deferred federal provision. These unutilized AMT credit carryforwards become partially refundable in 2019, 2020 and 2021 and fully refundable in 2022.

A reconciliation of the expected federal income tax at the statutory rate to the provision for income taxes was as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Expected federal income tax at statutory rate	$	3,107		$	3,011		$	2,404
State income taxes, net of federal tax effect		366			320			246
Tax impact of foreign activity		(105	)		(115	)		39
Permanent book/tax differences		460			372			67
Change in valuation allowance		16			(35	)		(27	)
Change in state deferred rate		(134	)		(67	)		(118	)
Research and development credit		(227	)		(261	)		(200	)
Tax impact of Tax Cuts and Jobs Act		8,613			—			—
Tax impact of stock activity		(925	)		—			—
Other		409			(85	)		25
Total provision for income taxes	$	11,580		$	3,140		$	2,436

The tax provision for the year ended December 31, 2017 includes tax benefits of $0.9 million for the excess tax deduction from stock activity. It also includes tax expense of $8.6 million related to The Job Cuts and Tax Act (“Tax Act”), primarily due to the reduction in corporate tax rate to 21.0% resulting in a decrease in our U.S. net deferred tax assets.

Differences between our effective tax rate and statutory tax rates are primarily due to the impact of the Tax Act, as well as permanently non-deductible expenses partially offset by the federal research and development credit. Additionally, under ASU 2016-09, excess tax benefits generated upon settlement or exercise of stock awards are now recognized as a reduction to income tax expense as a discrete tax item in the period that the event occurs creating potentially significant fluctuation in tax expense by year.

The significant components of our deferred tax assets (liabilities) were as follows (in thousands):

	December 31,
	2017						2016
Deferred tax assets
Net operating loss and credit carryforwards	$	11,067					$	4,614
Deferred operations		—						799
Stock-based compensation expense		4,273						4,085
Accounts receivable allowances		307						363
Accrued expenses		2,293						2,704
Other		182						297
Gross deferred tax asset					18,122						12,862
Less: valuation allowance		(602	)					(649	)
Total net deferred tax asset					17,520						12,213
Deferred tax liability
Deferred operations		(163	)					—
Foreign operations		(133	)					(350	)
Depreciation and amortization		(1,536	)					(1,328	)
Other		(24	)					—
Total deferred tax liability					(1,856	)					(1,678	)
Net deferred tax assets				$	15,664					$	10,535

As of December 31, 2017, we had net operating loss carryforwards of $58.5 million for U.S. federal tax purposes. We also had $10.6 million of various state net operating loss carryforwards. The loss carryforwards for federal tax purposes will expire between 2020 and 2036 if not utilized. The loss carryforwards for state tax purposes will expire between 2018 and 2036 if not utilized.

Section 382 of the U.S. Internal Revenue Code generally imposes an annual limitation on the amount of net operating loss carryforwards that might be used to offset taxable income when a corporation has undergone significant changes in stock ownership. We have performed a Section 382 analysis for the time period from our inception through December 8, 2010. During this time period it was determined that we had six separate ownership changes under Section 382. We have not updated the Section 382 analysis subsequent to December 8, 2010, however, we believe there have not been any events subsequent to that date that would materially impact the analysis. We believe that approximately $17.6 million of federal losses will expire unused due to Section 382 limitations. The maximum annual limitation of federal net operating losses under Section 382 is approximately $1.0 million. This limitation could be further restricted if any ownership changes occur in future years. Accordingly, our deferred tax assets are reported net of the excess tax deductions for stock compensation and Section 382 limitations.

As of December 31, 2017 we had federal research and development credit carryforwards, net of Section 383 limitations, of $1.2 million, which, if not utilized, will begin to expire in 2030. We had state research and development credit carryforwards of $0.6 million which, if not utilized, will begin to expire in 2025.

As of December 31, 2017, we had a valuation allowance against our deferred tax assets of $0.6 million. The valuation allowance is established for state net operating loss and credit carryforwards that we do not expect to utilize based on our current expectations of future state taxable income.

We are subject to income taxes in the U.S. federal, various state and international jurisdictions. We are generally subject to U.S. federal and state tax examinations for all prior tax years due to our net operating loss carryforwards and the utilization of the carryforwards in years still open under statute.

As of December 31, 2017, we do not have any unrecognized tax benefits. It is our practice to recognize interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. We do not expect any material changes in our unrecognized tax positions over the next 12 months.

Tax Act

The Tax Act, which was enacted on December 22, 2017, includes broad and complex changes to the U.S tax code. The Tax Act reduces the corporate federal income tax rate to 21.0% effective January 1, 2018 and establishes a mandatory tax on previously untaxed foreign earnings and profits (“E&P”). The Tax Act expands the limitations for executive compensation under Section 162(m) and includes transition rules for previously awarded compensation.

Accounting Standard Codification 740 requires a company to record the effects of a tax law change in the period of enactment, however, the SEC staff issued SAB 118, which allows a company to record a provisional amount when it does not have the necessary information available, prepared or analyzed in reasonable detail to complete its accounting for the change in the tax law. The measurement period ends when the company has obtained, prepared and analyzed the information necessary to finalize its accounting, but cannot extend beyond one year.

We have finalized our accounting for the corporate rate reduction and have recorded a decrease to our net deferred tax assets of $8.6 million with a corresponding adjustment to deferred tax expense for the year ended December 31, 2017. We have estimated that there is no tax on mandatory deemed repatriation due to a net foreign E&P deficit. We are continuing to evaluate the impact of the Tax Act on the taxation of previously untaxed foreign E&P and the deferred tax liability for withholding taxes on dividends. We are also continuing to evaluate the impact the expanded Section 162(m) limitations and related transition rules have on our deferred tax assets related to stock compensation.

Net Income (Loss) Per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

NOTE K – Net Income (Loss) Per Share

The following table presents the components of the computation of basic and diluted net income (loss) per share for the periods indicated (in thousands, except per share amounts):

	Year Ended December 31,
	2017			2016		2015
Numerator
Net (loss) income	$	(2,440	)	$	5,710	$	4,639
Denominator
Weighted average common shares outstanding, basic		17,183			16,947		16,565
Options to purchase common stock		—			267		437
Restricted stock units		—			27		27
Employee stock purchase plan		—			—		3
Weighted average common shares outstanding, diluted		17,183			17,241		17,032
Net (loss) income per share
Basic	$	(0.14	)	$	0.34	$	0.28
Diluted	$	(0.14	)	$	0.33	$	0.27

For the years ended December 31, 2017, 2016 and 2015, the effect of approximately 283,000, 5,000 and 4,000 outstanding potential common shares, respectively, were excluded from the calculation of diluted net income (loss) per share as they were anti-dilutive.

Retirement Savings Plan	12 Months Ended
Retirement Savings Plan	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Retirement Savings Plan	NOTE L – Retirement Savings Plan We sponsor a 401(k) retirement savings plan for our U.S. employees. Employees can contribute up to 100% of their compensation, subject to the limits established by law. We match 25% of the employee’s contribution up to the first 6% of pre-tax annual compensation. Additionally, we make statutory contributions to retirement plans as required by local foreign government regulations. Our contributions to the plans, which vest immediately, were $1.6 million, $1.4 million and $1.1 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	NOTE M – Related Party Transactions SPS Commerce Foundation (the “Foundation”) is a Minnesota non-profit organization exempt from federal taxation under Section 501(c)(3) of the Internal Revenue Code. The Foundation was formed in 2015 to engage in, advance, support, promote and administer charitable activities. The directors of the Foundation are also our officers. These officers receive no compensation from the Foundation for the management services performed for the Foundation. The Foundation is not a subsidiary of ours and the financial results of the Foundation are not consolidated with our financial statements. We made contributions of $0.2 million and $0.3 million to the Foundation for the years ended December 31, 2017 and 2016, respectively. We have no current legal obligations for future commitments to the Foundation.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

NOTE N – Selected Quarterly Financial Data (Unaudited)

The following table presents our selected unaudited quarterly statements of comprehensive income data (in thousands, except per share amounts):

	For the Three Months Ended
2017	Mar 31		Jun 30		Sep 30		Dec 31
Revenues	$	51,932	$	54,284	$	56,150	$	58,200
Gross profit		34,602		36,093		37,505		38,741
Income (loss) from operations		3,376		2,727		2,846		(521	)
Net income (loss)		2,971		1,825		1,865		(9,101	)
Diluted earnings (loss) per share	$	0.17	$	0.11	$	0.11	$	(0.53	)

	For the Three Months Ended
2016	Mar 31		Jun 30		Sep 30		Dec 31
Revenues	$	45,599	$	47,351	$	49,284	$	51,061
Gross profit		30,718		31,379		33,113		33,739
Income from operations		1,314		880		2,670		2,653
Net income		1,044		352		2,509		1,805
Diluted earnings per share	$	0.06	$	0.02	$	0.14	$	0.10

General (Policies)	12 Months Ended
General (Policies)	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of SPS Commerce, Inc. and its subsidiaries. All intercompany accounts and transactions have been eliminated in the consolidated financial statements.
Foreign Currency Translation	Foreign Currency Translation Assets and liabilities denominated in currencies other than the U.S. dollar are translated into U.S. dollars at the exchange rates in effect at the balance sheet date, with the resulting translation adjustments recorded as a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at the average exchange rates during the year. Foreign currency transaction gains and losses, if any, are included in net income (loss).
Use of Estimates	Use of Estimates Preparing financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.
Business Combinations	Business Combinations We recognize separately from goodwill the fair value of the assets acquired and the liabilities assumed at the acquisition date. Goodwill as of the acquisition date is measured as the excess of consideration transferred and the net of the acquisition date amounts of the assets acquired and the liabilities assumed. Assets acquired include tangible and intangible assets. We use estimates and assumptions that we believe are reasonable as a part of determining the value and useful lives of purchased intangible assets and the purchase price allocation process. While we believe these estimates and assumptions are reasonable, they are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, we may record adjustments to the fair value of the assets acquired and the liabilities assumed. Any such adjustments would be recorded as an offset to goodwill. Upon the conclusion of the measurement period or final determination of the fair values, whichever comes first, any subsequent adjustments would be recorded in our consolidated statements of comprehensive income.
Segment Information	Segment Information We operate in and report on one segment, which is supply chain management solutions.
Risk and Uncertainties	Risk and Uncertainties We rely on hardware and software licensed from third parties to offer our on-demand solutions. Our management believes alternate sources are available; however, disruption or termination of these relationships could adversely affect our operating results in the near term.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist principally of temporary cash and cash equivalents in financial institutions in excess of federally insured limits and trade accounts receivable. Temporary cash investments are held with financial institutions that we believe are subject to minimal risk.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of cash and highly liquid investments with original maturities of less than 90 days. Cash and cash equivalents are stated at fair value.
Investments	Investments Management determines the appropriate classification of certificates of deposit and marketable securities at the time of purchase and reevaluates such determination at each balance sheet date. Securities are classified as available for sale and are carried at fair value, with the change in unrealized gains and losses, net of tax, reported as a separate component on the consolidated statements of comprehensive income. Fair value is determined based on quoted market rates when observable or utilizing data points that are observable, such as quoted prices, interest rates and yield curves. When a determination has been made that an other-than-temporary decline in fair value has occurred, the amount of the decline that is related to a credit loss is realized and is included in other income (expense), net in the consolidated statements of comprehensive income.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of our financial instruments, which include cash, cash equivalents, accounts receivable, accounts payable and other accrued expenses, approximates fair value due to their short maturities. Marketable securities are recorded at fair value as further described in Note C.
Accounts Receivable	Accounts Receivable Accounts receivable are initially recorded upon the sale of solutions to customers. Credit is granted in the normal course of business without collateral. Accounts receivable are stated net of allowances for doubtful accounts, which represent estimated losses resulting from the inability of certain customers to make the required payments. When determining the allowances for doubtful accounts, we take several factors into consideration including the overall composition of the accounts receivable aging, our prior history of accounts receivable write-offs, the type of customers and our experience with specific customers. We write-off accounts receivable when they are determined to be uncollectible. Changes in the allowances for doubtful accounts are recorded as bad debt expense and are included in general and administrative expense in our consolidated statements of comprehensive income.
Property and Equipment	Property and Equipment Property and equipment, including assets acquired under capital lease obligations, are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives when placed in service, which are: Computer equipment and software: 2 to 3 years Office equipment and furniture: 5 to 7 years Leasehold improvements: the shorter of the useful life of the asset or the remaining term of the lease Significant additions or improvements extending asset lives beyond one year are capitalized, while repairs and maintenance are charged to expense as incurred. We also capitalize and amortize eligible costs to acquire or develop internal-use software that are incurred during the development stage. The assets and related accumulated depreciation and amortization are adjusted for asset retirements and disposals with the resulting gain or loss included in our consolidated statements of comprehensive income.
Research and Development	Research and Development Research and development costs primarily include maintenance and data conversion activities related to our cloud-based supply chain management solutions and are expensed as incurred.
Goodwill	Goodwill Goodwill represents the excess of the purchase price over the fair value of identifiable net assets acquired in business combinations. We test goodwill for impairment annually at November 30, or more frequently if events or changes in circumstances indicate that the asset might be impaired. The impairment test is conducted by comparing the fair value of the net assets with the carrying value of the reporting unit. Fair value is determined using the direct market observation of market price and outstanding equity of the reporting unit at the testing date. If the carrying value of the goodwill exceeds the fair value of the reporting unit, goodwill may be impaired. If this occurs, the fair value is then allocated to its assets and liabilities in a manner similar to a purchase price allocation in order to determine the implied fair value of goodwill. This implied fair value is then compared to the carrying amount of goodwill and, if it is less, we would recognize an impairment loss.
Intangible Assets	Intangible Assets Assets acquired in business combinations may include identifiable intangible assets such as subscriber relationships and non-competition agreements. We recognize separately from goodwill the fair value of the identifiable intangible assets acquired. We have determined the fair value and useful lives of our purchased intangible assets using certain estimates and assumptions that we believe are reasonable. The purchased intangible assets are being amortized on a straight-line basis over their estimated useful lives, which are three to nine years for subscriber relationships, two to five years for non-competition agreements and one to four years for technology and other.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We review our long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. The carrying amount of a long-lived asset is not recoverable if the carrying amount of an asset group exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the assets at the date it is tested for recoverability, whether in use or under development. An impairment loss is measured as the amount by which the carrying amount of a long-lived asset exceeds its fair value.
Revenue Recognition	Revenue Recognition We generate revenues by providing three types of solutions to our customers; fulfillment, enablement and analytics. Our cloud-based solutions allow our customers to meet their supply chain management requirements. Revenues are recognized when all of the following criteria are met: (1) persuasive evidence of an arrangement exists, (2) delivery has occurred, (3) the fee is fixed or determinable, and (4) collectability is probable. If collection is not considered probable, revenues are recognized when the fees are collected. Fees related to our fulfillment and analytics solutions consist of two revenue sources: set-up fees and recurring monthly fees. Set-up fees are specific for each connection a customer has with a trading partner and most of our customers have connections with numerous trading partners. Set-up fees are nonrefundable upfront fees that do not have standalone value to our customer and are not separable from the recurring monthly fees. All set-up fees and related costs are deferred and recognized ratably over the average life of the connection between the customer and the trading partner, which is approximately two years. We begin recognizing set-up fee revenue once the connection is established. Set-up fees for which connections have not yet been established are classified as long-term. We continue to evaluate the length of the amortization period as more experience is gained with cancellations and technology changes requested by our customers. It is possible that, in the future, the period over which such subscription set-up fees and costs are amortized may be adjusted. Any change in our estimate of the average connection life will affect our future results of operations. The recurring monthly fees are comprised of both fixed and transaction-based fees that are recognized as earned.
Stock-Based Compensation	Stock-Based Compensation We recognize the cost of all share-based payments to employees, including grants of employee stock options, in the financial statements based on the grant date fair value of those awards. This cost is recognized over the period for which an employee is required to provide service in exchange for the award. We estimate the fair value of options granted using the Black-Scholes option pricing model. In valuing share-based awards, judgment is required in determining the expected volatility of common stock and the expected term individuals will hold their share-based awards prior to exercising. The expected volatility of the options is based on the historical volatility of our common stock. The expected term of the options is based on the simplified method which does not consider historical employee exercise behavior.
Income Taxes	Income Taxes We account for income taxes using the liability method, which requires recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance when, in our judgement, there is a less than a 50% likelihood that the deferred tax asset will be utilized. We assess our ability to realize our deferred tax assets at the end of each reporting period. Realization of our deferred tax assets is contingent upon future taxable earnings. Accordingly, this assessment requires significant estimates and judgment. If the estimates of future taxable income vary from actual results, our assessment regarding the realization of these deferred tax assets could change. Future changes in the estimated amount of deferred taxes expected to be realized will be reflected in our consolidated financial statements in the period the estimate is changed, with a corresponding adjustment to our operating results. We recognize the financial statement benefit of a tax position only after determining that the relevant tax authority would “more likely than not” sustain the position following an audit. For tax positions meeting the “more likely than not” threshold, the amount recognized in the financial statements is the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement with the relevant tax authority.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net income (loss) per share has been computed using the weighted average number of shares of common stock outstanding during each period. Diluted net income (loss) per share also includes the impact of our outstanding potential common shares, including options, restricted stock units and restricted stock awards. Potential common shares that are anti-dilutive are excluded from the calculation of diluted net income (loss) per share.
Recently Adopted/Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”). The new guidance requires excess tax benefits and tax deficiencies to be recorded in the income statement when the awards vest or are settled and provides an accounting policy election to account for forfeitures as they occur. In addition, cash flows related to excess tax benefits will no longer be separately classified as a financing activity apart from other income tax cash flows within operating activities. The standard also allows entities to repurchase more of an employee’s shares for tax withholding purposes without triggering liability accounting and clarifies that all cash payments made on an employee’s behalf for withheld shares should be presented as a financing activity on the statements of cash flows. The standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, with early adoption permitted. We adopted ASU 2016-09 during the year ended December 31, 2017. The impact to our consolidated balance sheet as of January 1, 2017 was a $16.3 million increase in deferred income tax assets and a corresponding $16.3 million decrease in accumulated deficit. This impact results from the cumulative-effect adjustment for previously unrecognized excess tax benefits using the modified retrospective method required by the new standard. We elected to adopt the changes in cash flow statement presentation prospectively to be consistent with the prospective transition for the treatment of excess tax benefits in the income statement. Accordingly, we no longer classify excess tax benefits as a financing activity subsequent to January 1, 2017. On December 22, 2017, the Securities and Exchange Commission (“SEC”) staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP related to the enactment of the comprehensive tax legislation, commonly referred to as the Tax Cut and Jobs Act (“Tax Act”). This guidance was adopted in the fourth quarter of 2017. Additional information regarding our adoption of this guidance is contained in Note J. Recent Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance will replace most existing revenue recognition guidance in GAAP when it becomes effective. These new requirements are effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual periods. The new revenue recognition standard will not materially impact our recognition of the primary fees received from customers for our cloud-based supply chain solutions. The adoption of the new standard will impact our accounting for certain upfront set-up fees and the periods over which the related revenues are recognized, as well as the timing of cost recognition for some sales commissions. When compared to previously reported amounts, revenue will decrease $0.5 million and $0.1 million for the years ended December 31, 2017 and 2016, respectively. Commission expense, which is reported in sales and marketing expense, will decrease $2.0 million for the year ended December 31, 2017 and increase $1.0 million for the year ended December 31, 2016. In February 2016, the FASB issued ASU 2016-02, Leases, which will supersede existing lease guidance and will require all leases with a term greater than 12 months to be recognized in the statements of financial position and eliminate current real estate-specific lease guidance, while maintaining substantially similar classification criteria for distinguishing between finance leases and operating leases. This standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. We believe the adoption of the new lease accounting standard will materially impact our consolidated financial statements by increasing our non-current assets and non-current liabilities on our consolidated balance sheets in order to record the right of use assets and related lease liabilities for our existing operating leases. We are in the process of determining the financial statement impact and are currently unable to estimate the impact on our consolidated financial statements. In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), which simplifies the test for goodwill impairment by eliminating step two from the goodwill impairment test. Under the new guidance, an entity should recognize an impairment charge for the amount based on the excess of a reporting unit’s carrying amount over its fair value. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. This guidance is effective for annual and interim impairment tests performed in periods beginning after December 15, 2019 on a prospective basis, and earlier adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. We believe the adoption of this standard will not have a material impact on our consolidated financial statements.

Business Acquisitions (Tables)

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Business Purchase Price

The purchase price consisted of the following (in thousands):

Cash	$	18,032
SPS Commerce, Inc. common stock		2,922
Fair value of share-based earn-out liability		1,043
	$	21,997

Estimated Fair Values of Assets Acquired, Net of Cash Acquired and Liabilities Assumed at Acquisition Date

The following table summarizes the estimated fair values of the assets acquired, net of cash acquired of $0.4 million, and liabilities assumed at the acquisition date (in thousands):

Current assets	$	1,253
Property and equipment		56
Goodwill		15,389
Intangible assets		9,070
Current liabilities		(1,249	)
Deferred revenue		(301	)
Deferred income tax liability		(2,221	)
	$	21,997

Estimated Fair Value of Purchased Intangible Assets and Estimated Useful Lives

The following table summarizes the estimated fair value of the purchased intangible assets and their estimated useful lives:

	Estimated		Estimated
	Fair Value		Life
Purchased Intangible Assets	(in thousands)		(in years)
Subscriber relationships	$	7,400		8
Developed technology		1,200		4
Trade names		70		1
Non-competition agreements		400		5
Total	$	9,070

Pro Forma Financial Information

	Year Ended December 31,
(in thousands, except per share data)	2016		2015
Pro forma total revenue	$	193,525	$	166,873
Pro forma net income		5,976		2,400
Pro forma net income per share
Basic		0.35		0.14
Diluted		0.35		0.14

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Financial Instruments Owned At Fair Value [Abstract]

Summary of Cash Equivalents and Short and Long-term Investments

Cash equivalents and short- and long-term investments consisted of the following (in thousands):

	December 31,
	2017							2016
	Amortized		Unrealized			Fair		Amortized		Unrealized			Fair
	Cost		Gains (Losses)			Value		Cost		Gains (Losses)			Value
Cash equivalents:
Money market funds	$	104,544	$	—		$	104,544	$	75,375	$	—		$	75,375
Certificate of deposit		7,814		—			7,814		—		—			—
Marketable securities:
Corporate bonds		17,758		(57	)		17,701		15,681		(96	)		15,585
Commercial paper		7,456		20			7,476		4,977		10			4,987
U.S. treasury securities		12,381		26			12,407		7,489		10			7,499
U.S. agency obligations		—		—			—		2,497		3			2,500
	$	149,953	$	(11	)	$	149,942	$	106,019	$	(73	)	$	105,946
Due within one year						$	144,736						$	98,452
Due within two years							5,206							7,494
Total						$	149,942						$	105,946

Summary of Financial Assets Measured at Fair Value on a Recurring Basis

	Level 1		Level 2		Level 3		Total
Assets at December 31, 2017:
Cash equivalents:
Money market funds	$	104,544	$	—	$	—	$	104,544
Certificate of deposit		7,814		—		—		7,814
Marketable securities:
Corporate bonds		—		17,700		—		17,700
Commerical paper		—		7,477		—		7,477
U.S. treasury securities		—		12,407		—		12,407
	$	112,358	$	37,584	$	—	$	149,942
Assets at December 31, 2016:
Cash equivalents:
Money market funds	$	75,375	$	—	$	—	$	75,375
Marketable securities:
Corporate bonds		—		15,585		—		15,585
Commerical paper		—		4,987		—		4,987
U.S. treasury securities		—		7,499		—		7,499
U.S. agency obligations		—		2,500		—		2,500
	$	75,375	$	30,571	$	—	$	105,946

Allowance for Doubtful Accounts (Tables)

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

Schedule of Allowance for Doubtful Activity Included in Accounts Receivable Net

The allowance for doubtful accounts activity, included in accounts receivable, net, was as follows (in thousands):

	2017			2016			2015
Balances, January 1	$	515		$	446		$	279
Provision for doubtful accounts		1,705			1,375			1,271
Write-offs, net of recoveries		(1,457	)		(1,306	)		(1,104	)
Balances, December 31	$	763		$	515		$	446

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net included the following (in thousands):

	December 31,
	2017			2016
Computer equipment and software	$	35,326		$	29,270
Office equipment and furniture		7,439			7,087
Leasehold improvements		8,042			7,844
		50,807			44,201
Less: accumulated depreciation and amortization		(33,951	)		(28,887	)
	$	16,856		$	15,314

Goodwill and Intangible Assets, net (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Changes in Net Carrying Amount of Goodwill

The changes in the net carrying amount of goodwill for the years ended December 31, 2017 and 2016 are as follows (in thousands):

	2017		2016
Balances, January 1	$	49,777	$	33,848
Additions from business acquisitions		—		15,389
Foreign currency translation		1,836		540
Balances, December 31	$	51,613	$	49,777

Intangible Assets

Intangible assets, net included the following (in thousands):

	December 31, 2017
	Carrying Amount		Accumulated Amortization			Foreign Currency Translation		Net
Subscriber relationships	$	34,350	$	(19,592	)	$	614	$	15,372
Non-competition agreements		2,499		(2,058	)		45		486
Technology and other		2,130		(1,518	)		59		671
	$	38,979	$	(23,168	)	$	718	$	16,529

	December 31, 2016
	Carrying Amount		Accumulated Amortization			Foreign Currency Translation		Net
Subscriber relationships	$	33,736	$	(15,708	)	$	295	$	18,323
Non-competition agreements		2,234		(1,818	)		17		433
Technology and other		2,089		(1,120	)		63		1,032
	$	38,059	$	(18,646	)	$	375	$	19,788

Future Amortization Expense for Intangible Assets

At December 31, 2017, future amortization expense for intangible assets was as follows (in thousands):

2018	$	4,022
2019		3,730
2020		3,365
2021		2,520
2022		1,449
Thereafter		1,443
	$	16,529

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Future Minimum Payments Under Operating Leases

At December 31, 2017, our future minimum payments under operating leases were as follows (in thousands):

2018	$	3,833
2019		3,847
2020		3,122
2021		3,624
2022		3,270
Thereafter		6,796
	$	24,492

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation Expense

Stock-based compensation expense was allocated as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015
Cost of revenues	$	1,887	$	1,309	$	989
Operating expenses
Sales and marketing		2,197		2,412		1,978
Research and development		949		618		640
General and administrative		7,694		3,684		2,772
Total stock-based compensation expense	$	12,727	$	8,023	$	6,379

Stock Option Activity

Our stock option activity was as follows:

				Weighted Average
	Options			Exercise Price
	(#)			($/share)
Outstanding at January 1, 2015		1,085,463		$	26.53
Granted		181,487			67.50
Exercised		(305,106	)		14.55
Forfeited		(18,741	)		45.82
Outstanding at December 31, 2015		943,103			37.91
Granted		340,609			48.58
Exercised		(221,630	)		19.42
Forfeited		(46,070	)		55.58
Outstanding at December 31, 2016		1,016,012			44.72
Granted		172,697			55.87
Exercised		(65,502	)		21.53
Forfeited		(25,876	)		55.93
Outstanding at December 31, 2017		1,097,331			47.60

Weighted Average Fair Value Per Share of Options Granted, Assumptions

	Year Ended December 31,
	2017			2016			2015
Volatility		38	%		38	%		39	%
Dividend yield		—			—			—
Life (in years)		4.51			4.54			4.52
Risk-free interest rate		1.85	%		1.19	%		1.36	%

Fair Value Estimation of Common Stock Using Black-Scholes Option Pricing Model, Weighted-Average Assumptions

The fair value was estimated based on the market price of our common stock at the beginning of each offering period and using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2017			2016			2015
Volatility		32	%		37	%		30	%
Dividend yield		—			—			—
Life (in years)		0.50			0.50			0.50
Risk-free interest rate		0.90	%		0.42	%		0.12	%

Performance Share Units and Restricted Stock Units [Member]

Performance Share Units and Restricted Stock Units and Restricted Stock Awards

Our PSU and RSU activity was as follows:

				Weighted Average
	PSUs and RSUs			Grant Date Fair
	(#)			Value ($/share)
Outstanding at January 1, 2015		115,133		$	45.25
Granted		68,159			67.50
Vested and common stock issued		(37,669	)		40.91
Forfeited		(5,058	)		54.28
Outstanding at December 31, 2015		140,565			56.88
Granted		115,896			48.32
Vested and common stock issued		(52,133	)		48.19
Forfeited		(15,286	)		55.48
Outstanding at December 31, 2016		189,042			54.14
Granted		211,168			55.62
Vested and common stock issued		(64,950	)		53.64
Forfeited		(13,348	)		55.39
Outstanding at December 31, 2017		321,912			55.16

Restricted Stock Award [Member]

Performance Share Units and Restricted Stock Units and Restricted Stock Awards

Our RSA activity was as follows:

				Weighted Average
	RSAs			Grant Date Fair
	(#)			Value ($/share)
Outstanding at January 1, 2015		1,338		$	51.74
Restricted common stock issued		4,110			67.37
Restrictions lapsed		(4,416	)		62.63
Outstanding at December 31, 2015		1,032			67.39
Restricted common stock issued		6,078			52.27
Restrictions lapsed		(5,586	)		55.06
Outstanding at December 31, 2016		1,524			52.28
Restricted common stock issued		5,454			58.29
Restrictions lapsed		(5,610	)		56.65
Outstanding at December 31, 2017		1,368			58.29

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Provision for Income Taxes

Our provisions for income taxes included current federal, foreign and state income tax expense, as well as deferred tax expense as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Current
Federal	$	(184	)	$	3,684		$	2,066
State		258			555			289
Foreign		652			599			119
Deferred
Federal		11,551			(988	)		103
State		(342	)		(133	)		(141	)
Foreign		(355	)		(577	)		—
	$	11,580		$	3,140		$	2,436

Reconciliation of the Provision for Income Taxes to the Statutory Federal Rate

A reconciliation of the expected federal income tax at the statutory rate to the provision for income taxes was as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Expected federal income tax at statutory rate	$	3,107		$	3,011		$	2,404
State income taxes, net of federal tax effect		366			320			246
Tax impact of foreign activity		(105	)		(115	)		39
Permanent book/tax differences		460			372			67
Change in valuation allowance		16			(35	)		(27	)
Change in state deferred rate		(134	)		(67	)		(118	)
Research and development credit		(227	)		(261	)		(200	)
Tax impact of Tax Cuts and Jobs Act		8,613			—			—
Tax impact of stock activity		(925	)		—			—
Other		409			(85	)		25
Total provision for income taxes	$	11,580		$	3,140		$	2,436

Significant Components of Deferred Tax Assets (Liabilities)

The significant components of our deferred tax assets (liabilities) were as follows (in thousands):

	December 31,
	2017						2016
Deferred tax assets
Net operating loss and credit carryforwards	$	11,067					$	4,614
Deferred operations		—						799
Stock-based compensation expense		4,273						4,085
Accounts receivable allowances		307						363
Accrued expenses		2,293						2,704
Other		182						297
Gross deferred tax asset					18,122						12,862
Less: valuation allowance		(602	)					(649	)
Total net deferred tax asset					17,520						12,213
Deferred tax liability
Deferred operations		(163	)					—
Foreign operations		(133	)					(350	)
Depreciation and amortization		(1,536	)					(1,328	)
Other		(24	)					—
Total deferred tax liability					(1,856	)					(1,678	)
Net deferred tax assets				$	15,664					$	10,535

Net Income (Loss) Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Components of Computation of Basic and Diluted Net Income (Loss) Per Share

The following table presents the components of the computation of basic and diluted net income (loss) per share for the periods indicated (in thousands, except per share amounts):

	Year Ended December 31,
	2017			2016		2015
Numerator
Net (loss) income	$	(2,440	)	$	5,710	$	4,639
Denominator
Weighted average common shares outstanding, basic		17,183			16,947		16,565
Options to purchase common stock		—			267		437
Restricted stock units		—			27		27
Employee stock purchase plan		—			—		3
Weighted average common shares outstanding, diluted		17,183			17,241		17,032
Net (loss) income per share
Basic	$	(0.14	)	$	0.34	$	0.28
Diluted	$	(0.14	)	$	0.33	$	0.27

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summary of Unaudited Quarterly Statements of Comprehensive Income Data

The following table presents our selected unaudited quarterly statements of comprehensive income data (in thousands, except per share amounts):

	For the Three Months Ended
2017	Mar 31		Jun 30		Sep 30		Dec 31
Revenues	$	51,932	$	54,284	$	56,150	$	58,200
Gross profit		34,602		36,093		37,505		38,741
Income (loss) from operations		3,376		2,727		2,846		(521	)
Net income (loss)		2,971		1,825		1,865		(9,101	)
Diluted earnings (loss) per share	$	0.17	$	0.11	$	0.11	$	(0.53	)

	For the Three Months Ended
2016	Mar 31		Jun 30		Sep 30		Dec 31
Revenues	$	45,599	$	47,351	$	49,284	$	51,061
Gross profit		30,718		31,379		33,113		33,739
Income from operations		1,314		880		2,670		2,653
Net income		1,044		352		2,509		1,805
Diluted earnings per share	$	0.06	$	0.02	$	0.14	$	0.10

General - Additional Information (Detail) $ in Millions	12 Months Ended
General - Additional Information (Detail) $ in Millions	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Jan. 01, 2017 USD ($)
Schedule Of Accounting Policies [Line Items]
Number of reportable segments \| Segment	1
Average life of connection between customer and trading partner	2 years
ASU 2016-09 [Member] \| Deferred Income Tax Assets, Non-Current [Member]
Schedule Of Accounting Policies [Line Items]
Cumulative effect of change due to new accounting pronouncement			$ (16.3)
ASU 2016-09 [Member] \| Accumulated Deficit [Member]
Schedule Of Accounting Policies [Line Items]
Cumulative effect of change due to new accounting pronouncement			$ 16.3
ASU 2014-09 [Member]
Schedule Of Accounting Policies [Line Items]
Decrease in revenue	$ 0.5	$ 0.1
ASU 2014-09 [Member] \| Sales and Marketing Expense [Member]
Schedule Of Accounting Policies [Line Items]
Increase (decrease) in commission expense	$ (2.0)	$ 1.0
Minimum [Member] \| Subscriber Relationships [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of intangible assets	3 years
Minimum [Member] \| Non-competition Agreements [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of intangible assets	2 years
Minimum [Member] \| Technology and Other [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of intangible assets	1 year
Maximum [Member] \| Subscriber Relationships [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of intangible assets	9 years
Maximum [Member] \| Non-competition Agreements [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of intangible assets	5 years
Maximum [Member] \| Technology and Other [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of intangible assets	4 years
Computer Equipment and Software [Member] \| Minimum [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of property and equipment	2 years
Computer Equipment and Software [Member] \| Maximum [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of property and equipment	3 years
Office Equipment and Furniture [Member] \| Minimum [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of property and equipment	5 years
Office Equipment and Furniture [Member] \| Maximum [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful lives of property and equipment	7 years

Business Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Jan. 05, 2016	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Stock issued for acquisition						$ 2,922
Amortization expense for purchased intangible assets				$ 4,574		4,738	$ 3,307
Toolbox Solutions, Inc. [Member]
Business Acquisition [Line Items]
Payments to acquire business	$ 18,032
Stock issued for acquisition	$ 2,922
Stock issued for acquisition, shares	43,953		43,953
Number of shares of common stock issuable	16,222
Number of gross shares issued	48,668
Number of shares returned from escrow		8,866	4,715
Cash acquired from acquisition	$ 400
Amortization expense for purchased intangible assets					$ 1,400
Acquisition-related costs						100
Revenues from acquisition					$ 7,900
Proforma adjustments in amortization						$ 1,400
Statutory blended income tax rate						26.50%
Toolbox Solutions, Inc. [Member] \| Contingent Consideration Liability [Member]
Business Acquisition [Line Items]
Other income						$ 1,100

Business Acquisitions - Business Purchase Price (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jan. 05, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
SPS Commerce, Inc. common stock		$ 2,922
Toolbox Solutions, Inc. [Member]
Business Acquisition [Line Items]
Cash	$ 18,032
SPS Commerce, Inc. common stock	2,922
Fair value of share-based earn-out liability	1,043
Total purchase price	$ 21,997

Business Acquisitions - Estimated Fair Values of the Assets Acquired, Net of Cash acquired and Liabilities Assumed at the Acquisition Date (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net
Goodwill	$ 51,613	$ 49,777	$ 33,848
Toolbox Solutions, Inc. [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net
Current assets	1,253
Property and equipment	56
Goodwill	15,389
Intangible assets	9,070
Current liabilities	(1,249)
Deferred revenue	(301)
Deferred income tax liability	(2,221)
Total purchase price	$ 21,997

Business Acquisitions - Estimated Fair Value of Purchased Intangible Assets and Estimated Useful Lives (Detail) - Toolbox Solutions, Inc. [Member] $ in Thousands	Jan. 05, 2016 USD ($)
Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 9,070
Subscriber Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 7,400
Estimated Life (in years)	8 years
Developed Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 1,200
Estimated Life (in years)	4 years
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 70
Estimated Life (in years)	1 year
Non-competition Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 400
Estimated Life (in years)	5 years

Business Acquisitions - Pro Forma Financial Information (Detail) - Toolbox Solutions, Inc. [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Pro forma total revenue	$ 193,525	$ 166,873
Pro forma net income	$ 5,976	$ 2,400
Pro forma net income per share, Basic	$ 0.35	$ 0.14
Pro forma net income per share, Diluted	$ 0.35	$ 0.14

Financial Instruments - Summary of Cash Equivalents and Short and Long-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial Instruments [Member]
Schedule of Financial Instruments [Line Items]
Due within one year	$ 144,736	$ 98,452
Amortized Cost	149,953	106,019
Due within two years	5,206	7,494
Unrealized Gains (Losses)	(11)	(73)
Fair Value	149,942	105,946
Money Market Funds [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	104,544	75,375
Fair Value	104,544	75,375
Certificate of Deposit [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	7,814
Fair Value	7,814
Corporate Bonds [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	17,758	15,681
Unrealized Gains (Losses)	(57)	(96)
Fair Value	17,701	15,585
Commercial Paper [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	7,456	4,977
Unrealized Gains (Losses)	20	10
Fair Value	7,476	4,987
U.S. Treasury Securities [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	12,381	7,489
Unrealized Gains (Losses)	26	10
Fair Value	$ 12,407	7,499
U.S. Agency Obligations [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost		2,497
Unrealized Gains (Losses)		3
Fair Value		$ 2,500

Financial Instruments - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	$ 149,942	$ 105,946
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	104,544	75,375
Certificate of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	7,814
Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	17,700	15,585
Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	7,477	4,987
U.S. Treasury Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	12,407	7,499
U.S. Agency Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value		2,500
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	112,358	75,375
Level 1 [Member] \| Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	104,544	75,375
Level 1 [Member] \| Certificate of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	7,814
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	37,584	30,571
Level 2 [Member] \| Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	17,700	15,585
Level 2 [Member] \| Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	7,477	4,987
Level 2 [Member] \| U.S. Treasury Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	$ 12,407	7,499
Level 2 [Member] \| U.S. Agency Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value		$ 2,500

Allowance for Doubtful Accounts - Schedule of Allowance for Doubtful Activity Included in Accounts Receivable Net (Detail) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation And Qualifying Accounts Disclosure [Line Items]
Balances, January 1	$ 515	$ 446	$ 279
Provision for doubtful accounts	1,705	1,375	1,271
Write-offs, net of recoveries	(1,457)	(1,306)	(1,104)
Balances, December 31	$ 763	$ 515	$ 446

Property and Equipment, net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 50,807	$ 44,201
Less: accumulated depreciation and amortization	(33,951)	(28,887)
Net, Total	16,856	15,314
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	35,326	29,270
Office Equipment and Furniture [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	7,439	7,087
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 8,042	$ 7,844

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Outside of U.S [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment, net held at subsidiary and office locations outside of the U.S.	$ 2.2	$ 2.1

Goodwill and Intangible Assets, net - Schedule of Changes in Net Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Balances, January 1	$ 49,777	$ 33,848
Additions from business acquisitions		15,389
Foreign currency translation	1,836	540
Balances, December 31	$ 51,613	$ 49,777

Goodwill and Intangible Assets, net - Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Carrying Amount	$ 38,979	$ 38,059
Accumulated Amortization	(23,168)	(18,646)
Foreign Currency Translation	718	375
Net	16,529	19,788
Subscriber Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Carrying Amount	34,350	33,736
Accumulated Amortization	(19,592)	(15,708)
Foreign Currency Translation	614	295
Net	15,372	18,323
Non-competition Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Carrying Amount	2,499	2,234
Accumulated Amortization	(2,058)	(1,818)
Foreign Currency Translation	45	17
Net	486	433
Technology and Other [Member]
Finite-Lived Intangible Assets [Line Items]
Carrying Amount	2,130	2,089
Accumulated Amortization	(1,518)	(1,120)
Foreign Currency Translation	59	63
Net	$ 671	$ 1,032

Goodwill and Intangible Assets, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]
Amortization expense	$ 4,574	$ 4,738	$ 3,307

Goodwill and Intangible Assets, net - Future Amortization Expense for Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
2018	$ 4,022
2019	3,730
2020	3,365
2021	2,520
2022	1,449
Thereafter	1,443
Net	$ 16,529	$ 19,788

Commitments and Contingencies - Additional Information (Detail) $ in Millions		12 Months Ended
	Dec. 20, 2017 USD ($) ft² Option	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2020 ft²	Dec. 31, 2018 ft²
Commitments And Contingencies [Line Items]
Rent expense charged to operations \| $		$ 4.9	$ 5.0	$ 4.6
Current Headquarters [Member]
Commitments And Contingencies [Line Items]
Lease agreement expires, date	Apr. 30, 2025
Number of options to extend term of the lease \| Option	2
Lease extension period, number of years	5 years
Incentives received upon execution of amendment \| $	$ 3.2
Current Headquarters [Member] \| Minneapolis, Minnesota [Member]
Commitments And Contingencies [Line Items]
Current leased space for headquarters \| ft²	166,000
Current Headquarters [Member] \| Scenario, Forecast [Member] \| Minneapolis, Minnesota [Member]
Commitments And Contingencies [Line Items]
Future expansion of headquarters premises \| ft²					48,000	48,000

Commitments and Contingencies - Future Minimum Payments Under Operating Leases (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 3,833
2019	3,847
2020	3,122
2021	3,624
2022	3,270
Thereafter	6,796
Operating leases, total	$ 24,492

Stockholders' Equity - Additional Information (Detail) - USD ($) $ in Thousands			3 Months Ended			12 Months Ended
	Nov. 02, 2017	Jan. 05, 2016	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Stockholders Equity [Line Items]
Treasury stock at cost						$ 5,815
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Stock issued for acquisition, Shares							43,953
Stock repurchase program, authorized amount	$ 50,000
Stock repurchase program, period	2 years
Repurchase of treasury shares			122,147			(122,147)
Treasury stock at cost			$ 5,800
Stock repurchase program, available for future repurchases			$ 44,200			$ 44,200
Toolbox Solutions, Inc. [Member]
Schedule Of Stockholders Equity [Line Items]
Stock issued for acquisition, Shares		43,953			43,953
Number of gross shares issued		48,668
Number of shares returned from escrow				8,866	4,715
Fair value of the shares issued		$ 2,900

Stock-Based Compensation - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Feb. 28, 2017 shares	Dec. 31, 2017 USD ($) Offering $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Feb. 29, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant \| shares		4,600,000
Stock-based compensation expense		$ 12,727,000	$ 8,023,000	$ 6,379,000
Unrecognized stock-based compensation expense		$ 11,600,000
Unrecognized stock-based compensation, expected to be recognized, weighted average period		2 years 6 months
Stock options exercisable \| shares		743,471
Weighted average exercise price \| $ / shares		$ 44.58
Weighted average remaining contractual life		4 years
Fair value of options vested		$ 4,200,000	3,400,000	3,100,000
Intrinsic value of options exercised		2,800,000	8,600,000	16,800,000
Intrinsic value of options outstanding		$ 7,300,000	$ 25,600,000	$ 30,500,000
Weighted average fair value per share of options granted \| $ / shares		$ 18.85	$ 16.13	$ 23.09
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares reserved for issuance under the plan \| shares		1,000,000
Stock-based compensation expense		$ 700,000	$ 600,000	$ 400,000
Purchase price as a percentage of fair market value		85.00%
Number of offerings per year \| Offering		2
Amount withheld from employees		$ 1,900,000	$ 1,700,000	$ 1,500,000
Shares purchased \| shares		40,968	33,357	28,362
Chief Executive Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 3,600,000
Equity Incentive Plan [Member] \| 2010 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares reserved for issuance under the plan \| shares	1,024,868				1,003,439
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Stock Options [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options contractual term range		7 years
Stock Options [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options contractual term range		10 years
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 0
Vesting period	3 years
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards units vest over, period		1 year
Performance Share Units and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSU's vested and not issued during the period \| shares		44,177

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 12,727	$ 8,023	$ 6,379
Cost of Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,887	1,309	989
Sales and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,197	2,412	1,978
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	949	618	640
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 7,694	$ 3,684	$ 2,772

Stock-Based Compensation - Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance	1,016,012	943,103	1,085,463
Options, Granted	172,697	340,609	181,487
Options, Exercised	(65,502)	(221,630)	(305,106)
Options, Forfeited	(25,876)	(46,070)	(18,741)
Options Outstanding, Ending balance	1,097,331	1,016,012	943,103
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 44.72	$ 37.91	$ 26.53
Weighted Average Exercise Price, Granted	55.87	48.58	67.50
Weighted Average Exercise Price, Exercised	21.53	19.42	14.55
Weighted Average Exercise Price, Forfeited	55.93	55.58	45.82
Weighted Average Exercise Price, Outstanding, Ending Balance	$ 47.60	$ 44.72	$ 37.91

Stock-Based Compensation - Weighted Average Fair Value Per Share of Options Granted, Assumptions (Detail) - Stock Options [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	38.00%	38.00%	39.00%
Dividend yield	0.00%	0.00%	0.00%
Life (in years)	4 years 6 months 3 days	4 years 6 months 15 days	4 years 6 months 7 days
Risk-free interest rate	1.85%	1.19%	1.36%

Stock-Based Compensation - Performance Share Units and Restricted Stock Units (Detail) - Performance Share Units and Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards, Outstanding, Beginning Balance	189,042	140,565	115,133
Granted, stock units	211,168	115,896	68,159
Vested and common stock issued, stock units	(64,950)	(52,133)	(37,669)
Forfeited, stock units	(13,348)	(15,286)	(5,058)
Stock awards, Outstanding, Ending Balance	321,912	189,042	140,565
Weighted average grant date fair value, Outstanding, Beginning Balance	$ 54.14	$ 56.88	$ 45.25
Granted, Weighted Average Grant Date Fair Value	55.62	48.32	67.50
Vested and common stock issued, Weighted Average Grant Date Fair Value	53.64	48.19	40.91
Forfeited, Weighted Average Grant Date Fair Value	55.39	55.48	54.28
Weighted average grant date fair value, Outstanding, Ending Balance	$ 55.16	$ 54.14	$ 56.88

Stock-Based Compensation - Restricted Stock Awards (Detail) - Restricted Stock Award [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards, Outstanding, Beginning Balance	1,524	1,032	1,338
Restricted common stock issued, stock awards	5,454	6,078	4,110
Restrictions lapsed, stock awards	(5,610)	(5,586)	(4,416)
Stock awards, Outstanding, Ending Balance	1,368	1,524	1,032
Weighted average grant date fair value, Outstanding, Beginning Balance	$ 52.28	$ 67.39	$ 51.74
Restricted common stock issued, Weighted Average Grant Date Fair Value	58.29	52.27	67.37
Restrictions lapsed, Weighted Average Grant Date Fair Value	56.65	55.06	62.63
Weighted average grant date fair value, Outstanding, Ending Balance	$ 58.29	$ 52.28	$ 67.39

Stock-Based Compensation - Fair Value Estimation of Common Stock Using Black-Scholes Option Pricing Model, Weighted-Average Assumptions (Detail) - Employee Stock Purchase Plan [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	32.00%	37.00%	30.00%
Dividend yield	0.00%	0.00%	0.00%
Life (in years)	6 months	6 months	6 months
Risk-free interest rate	0.90%	0.42%	0.12%

Income Taxes - Schedule of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal	$ (184)	$ 3,684	$ 2,066
State	258	555	289
Foreign	652	599	119
Deferred
Federal	11,551	(988)	103
State	(342)	(133)	(141)
Foreign	(355)	(577)
Total provision for income taxes	$ 11,580	$ 3,140	$ 2,436

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense Benefit [Line Items]
Reclass of AMT credit carryforward to current federal expense		$ 400,000
Unutilized alternative minimum tax credit carryforwards partially refundable year one		2019
Unutilized alternative minimum tax credit carryforwards partially refundable year two		2020
Unutilized alternative minimum tax credit carryforwards partially refundable year three		2021
Unutilized alternative minimum tax credit carryforwards fully refundable year		2022
Tax benefits for excess tax deduction from stock activity		$ 925,000
Tax expense related to The Job Cuts and Tax Act (“Tax Act”), primarily due to reduction in corporate tax rate		8,613,000
Valuation allowance against our deferred tax assets		602,000	$ 649,000
Decrease to net deferred tax assets		8,600,000
Estimated tax on mandatory deemed repatriation due to net foreign E&P deficit		0
Domestic Tax Authority [Member]
Income Tax Expense Benefit [Line Items]
Net operating loss carryforward		$ 58,500,000
Expiration of net operating loss carryforwards		Loss carryforwards for federal tax purposes will expire between 2020 and 2036 if not utilized
Losses expected to expire unused		$ 17,600,000
Maximum annual limitation of federal net operating losses		1,000,000
Domestic Tax Authority [Member] \| Research and Development [Member]
Income Tax Expense Benefit [Line Items]
Research and development credit carryforwards		$ 1,200,000
Year in which credit carryforward begins to expire		2030
State and Local Jurisdiction [Member]
Income Tax Expense Benefit [Line Items]
Net operating loss carryforward		$ 10,600,000
Expiration of net operating loss carryforwards		Loss carryforwards for state tax purposes will expire between 2018 and 2036 if not utilized
State and Local Jurisdiction [Member] \| Net Operating Loss and Credit Carryforwards [Member]
Income Tax Expense Benefit [Line Items]
Valuation allowance against our deferred tax assets		$ 600,000
State and Local Jurisdiction [Member] \| Research and Development [Member]
Income Tax Expense Benefit [Line Items]
Research and development credit carryforwards		$ 600,000
Year in which credit carryforward begins to expire		2025
Scenario, Forecast [Member]
Income Tax Expense Benefit [Line Items]
Corporate federal income tax rate	21.00%

Income Taxes - Reconciliation of Provision for Income Taxes to Statutory Federal Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected federal income tax at statutory rate	$ 3,107	$ 3,011	$ 2,404
State income taxes, net of federal tax effect	366	320	246
Tax impact of foreign activity	(105)	(115)	39
Permanent book/tax differences	460	372	67
Change in valuation allowance	16	(35)	(27)
Change in state deferred rate	(134)	(67)	(118)
Research and development credit	(227)	(261)	(200)
Tax impact of Tax Cuts and Jobs Act	8,613
Tax impact of stock activity	(925)
Other	409	(85)	25
Total provision for income taxes	$ 11,580	$ 3,140	$ 2,436

Income Taxes - Significant Components of Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Net operating loss and credit carryforwards	$ 11,067	$ 4,614
Deferred operations		799
Stock-based compensation expense	4,273	4,085
Accounts receivable allowances	307	363
Accrued expenses	2,293	2,704
Other	182	297
Gross deferred tax asset	18,122	12,862
Less: valuation allowance	(602)	(649)
Total net deferred tax asset	17,520	12,213
Deferred tax liability
Deferred operations	(163)
Foreign operations	(133)	(350)
Depreciation and amortization	(1,536)	(1,328)
Other	(24)
Total deferred tax liability	(1,856)	(1,678)
Net deferred tax assets	$ 15,664	$ 10,535

Net Income (Loss) Per Share - Components of Computation of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator
Net income (loss)	$ (9,101)	$ 1,865	$ 1,825	$ 2,971	$ 1,805	$ 2,509	$ 352	$ 1,044	$ (2,440)	$ 5,710	$ 4,639
Denominator
Weighted average common shares outstanding, basic									17,183	16,947	16,565
Options to purchase common stock										267	437
Restricted stock units										27	27
Employee stock purchase plan											3
Weighted average common shares outstanding, diluted									17,183	17,241	17,032
Net (loss) income per share
Basic									$ (0.14)	$ 0.34	$ 0.28
Diluted	$ (0.53)	$ 0.11	$ 0.11	$ 0.17	$ 0.10	$ 0.14	$ 0.02	$ 0.06	$ (0.14)	$ 0.33	$ 0.27

Net Income (Loss) Per Share - Additional Information (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net (loss) income per share
Outstanding potential common shares excluded from calculation of diluted net income (loss) per share	283	5	4

Retirement Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Maximum allowable contribution by employee percentage	100.00%
Defined benefit plan employer matching contribution percent	25.00%
Maximum annual contribution per employee, percent	6.00%
Employer matching contribution amount	$ 1.6	$ 1.4	$ 1.1

Related Party Transactions - Additional Information (Detail) - SPS Commerce Foundation [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Contributions to Foundation	$ 200,000	$ 300,000
Legal obligations for future commitments to Foundation	0
Directors of Foundation [Member]
Related Party Transaction [Line Items]
Officers' compensation from Foundation	$ 0

Selected Quarterly Financial Data (Unaudited) - Summary of Unaudited Quarterly Statements of Comprehensive Income Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 58,200	$ 56,150	$ 54,284	$ 51,932	$ 51,061	$ 49,284	$ 47,351	$ 45,599	$ 220,566	$ 193,295	$ 158,518
Gross profit	38,741	37,505	36,093	34,602	33,739	33,113	31,379	30,718	146,941	128,949	108,475
Income (loss) from operations	(521)	2,846	2,727	3,376	2,653	2,670	880	1,314	8,428	7,517	7,023
Net income (loss)	$ (9,101)	$ 1,865	$ 1,825	$ 2,971	$ 1,805	$ 2,509	$ 352	$ 1,044	$ (2,440)	$ 5,710	$ 4,639
Diluted earnings (loss) per share	$ (0.53)	$ 0.11	$ 0.11	$ 0.17	$ 0.10	$ 0.14	$ 0.02	$ 0.06	$ (0.14)	$ 0.33	$ 0.27