| Cover | Sep. 29, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 29, 2020 |
| Entity Registrant Name | Infinity Pharmaceuticals, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-31141 |
| Entity Tax Identification Number | 33-0655706 |
| Entity Address, Address Line One | 1100 Massachusetts Avenue |
| Entity Address, Address Line Two | Floor 4 |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02138 |
| City Area Code | 617 |
| Local Phone Number | 453-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value |
| Trading Symbol | INFI |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001113148 |
