| Cover Page - USD ($) | 12 Months Ended | ||
| Dec. 31, 2021 | Apr. 25, 2022 | Jun. 30, 2021 | |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Document Annual Report | true | ||
| Document Period End Date | Dec. 31, 2021 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document Transition Report | false | ||
| Entity File Number | 001-36289 | ||
| Entity Registrant Name | GENOCEA BIOSCIENCES, INC. | ||
| Entity Incorporation, State or Country Code | DE | ||
| Entity Tax Identification Number | 51-0596811 | ||
| Entity Address, Address Line One | 100 Acorn Park Drive | ||
| Entity Address, City or Town | Cambridge | ||
| Entity Address, State or Province | MA | ||
| Entity Address, Postal Zip Code | 02140 | ||
| City Area Code | 617 | ||
| Local Phone Number | 876-8191 | ||
| Title of 12(b) Security | Common Stock, $0.001 par value | ||
| Trading Symbol | GNCA | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Voluntary Filers | No | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Filer Category | Non-accelerated Filer | ||
| Entity Small Business | true | ||
| Entity Emerging Growth Company | false | ||
| Entity Shell Company | false | ||
| Entity Common Stock, Shares Outstanding | 58,783,503 | ||
| Entity Central Index Key | 0001457612 | ||
| Document Fiscal Year Focus | 2021 | ||
| Amendment Flag | false | ||
| Document Fiscal Period Focus | FY | ||
| Security Exchange Name | NASDAQ | ||
| Entity Public Float | $ 108,805,512 | ||
| Auditor Firm ID | 42 | ||
| Auditor Name | Ernst & Young LLP | ||
| Auditor Location | Boston, Massachusetts |
