Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Oct. 18, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol SPSC  
Entity Registrant Name SPS COMMERCE INC  
Entity Central Index Key 0001092699  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   34,839,275
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Shell Company false  
Entity File Number 001-34702  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 41-2015127  
Entity Address, Address Line One 333 South Seventh Street  
Entity Address, Address Line Two Suite 1000  
Entity Address, City or Town Minneapolis  
Entity Address, State or Province MN  
Entity Address, Postal Zip Code 55402  
City Area Code 612  
Local Phone Number 435-9400  
Title of 12(b) Security Common Stock, par value $0.001 per share  
Security Exchange Name NASDAQ  
Document Quarterly Report true  
Document Transition Report false