| Document and Entity Information | Nov. 04, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | SPS COMMERCE INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001092699 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Nov. 4, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-34702 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common stock, par value $0.001 per share |
| Trading Symbol | SPSC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
