Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 19, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
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   17,441,603
Entity Current Reporting Status Yes  
Entity Shell Company false  
Entity File Number 001-34702  
Entity Tax Identification Number 412015127  
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