Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2018
Feb. 08, 2019
Jun. 29, 2018
Document And Entity Information [Abstract]      
Document Type 10-K/A    
Amendment Flag true    
Amendment Description This Amendment No. 1 on Form 10-K/A amends the SPS Commerce, Inc. (the “Company”) Annual Report on Form 10-K for the fiscal year ending December 31, 2018, as filed with the Securities and Exchange Commission (“SEC”) on February 22, 2019 (the “Original Filing”). We are filing this Amendment No. 1 for the sole purpose of correcting a typographical error in Item 6. Selected Financial Data and Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations. Within the operating data table of Item 6, the table in footnote 3 of Item 6, and the reconciliation of net income to non-GAAP income per share table in Item 7, the Income tax effects of adjustments was inadvertently reported as $(4,468,000), with the corresponding Non-GAAP income with tax adjustments reported as $36,101,000 and the corresponding Non-GAAP income per share reported as $2.10 (basic) and $2.05 (diluted). The correct numbers are: •Income tax effects of adjustments: $(6,594,000) •Non-GAAP income: $33,975,000 •Non-GAAP income per share: $1.98 (basic) and $1.93 (diluted) The correct numbers appeared in our press release dated February 12, 2019, which was filed as Exhibit 99 to our Current Report on Form 10-K. This Form 10-K/A does not reflect events occurring after the Original Filing and does not modify or update in any way the disclosures contained in the Original Filing except as set forth above. Accordingly, this Amendment No. 1 should be read in conjunction with our filings with the SEC subsequent to the date of the Original Filing. As required by Rule 12b-15 under the Securities Exchange Act of 1934, new certificates of our principal executive officer and principal financial officer are being filed as exhibits to this Amendment No. 1 on Form 10-K/A.    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
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 Shell Company false    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock, Shares Outstanding   17,760,003  
Entity Public Float     $ 1.3