| Document and Entity Information | Jan. 11, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 11, 2021 |
| Entity Registrant Name | IMPINJ INC |
| Entity Central Index Key | 0001114995 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, State or Province | WA |
| Entity File Number | 001-37824 |
| Entity Tax Identification Number | 91-2041398 |
| Entity Address, Address Line One | 400 Fairview Avenue North |
| Entity Address, Address Line Two | Suite 1200 |
| Entity Address, City or Town | Seattle |
| Entity Address, Postal Zip Code | 98109 |
| City Area Code | (206) |
| Local Phone Number | 517-5300 |
| 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 | PI |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
