| Cover Cover | Sep. 30, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 30, 2021 |
| Entity Registrant Name | Stamps.com Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-26427 |
| Entity Tax Identification Number | 77-0454966 |
| Entity Address, Address Line One | 1990 E. Grand Avenue |
| Entity Address, City or Town | El Segundo, |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 90245 |
| City Area Code | (310) |
| Local Phone Number | 482-5800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Trading Symbol | STMP |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001082923 |
| Amendment Flag | false |
