| Cover Page - shares | 3 Months Ended | |
| Mar. 31, 2022 | Apr. 29, 2022 | |
| Cover [Abstract] | ||
| Document Type | 10-Q/A | |
| Document Quarterly Report | true | |
| Document Period End Date | Mar. 31, 2022 | |
| Document Transition Report | false | |
| Entity File Number | 001-39634 | |
| Entity Registrant Name | Foghorn Therapeutics Inc. | |
| Entity Incorporation, State | DE | |
| Entity Tax Identification Number | 47-5271393 | |
| Entity Address, Street Name | 500 Technology Square, Ste 700 | |
| Entity Address, City | Cambridge | |
| Entity Address, State | MA | |
| Entity Address, Postal Zip Code | 02139 | |
| City Area Code | 617 | |
| Local Phone Number | 586-3100 | |
| Title of each class | Common Stock, $0.0001 par value per share | |
| Trading Symbol(s) | FHTX | |
| Name of each exchange on which registered | NASDAQ | |
| Entity Current Reporting Status | Yes | |
| Entity Interactive Data Current | Yes | |
| Entity Filer Category | Non-accelerated Filer | |
| Entity Small Business | true | |
| Entity Emerging Growth Company | true | |
| Entity Ex Transition Period | false | |
| Entity Shell Company | false | |
| Entity Common Stock, Shares Outstanding | 41,467,808 | |
| Amendment Flag | true | |
| Document Fiscal Year Focus | 2022 | |
| Document Fiscal Period Focus | Q1 | |
| Entity Central Index Key | 0001822462 | |
| Current Fiscal Year End Date | --12-31 | |
| Amendment Description | EXPLANATORY NOTEFoghorn Therapeutics Inc. (the “Company”) is filing this Amendment No. 1 (this “Amendment”) on Form 10-Q/A to amend its Quarterly Report on Form 10-Q for the quarter ended March 31, 2022, filed with the Securities and Exchange Commission on May 9, 2022 (the “Original 10-Q”), for the purpose of filing revised versions of Exhibits 31.1 and 31.2 filed with the Original 10-Q.The Company is filing revised exhibits solely in order to include in the certifications set forth in the Exhibits the language added to the introductory portion of paragraph 4 and the language of revised paragraph 4(b), which language was inadvertently omitted from the certifications when originally filed. This Amendment does not reflect events occurring after the date of the filing of the Original 10-Q or modify or update any of the other disclosures contained therein in any way. Accordingly, this Amendment should be read in conjunction with the Original 10-Q. This Amendment consists solely of the preceding cover page, this Explanatory Note, the signature page and paragraphs 1, 2, 4 and 5 of each of the revised certifications filed as exhibits to the Amendment. Because no financial statements have been include in this Amendment, paragraph 3 of each of the certifications set forth in the Exhibits has been omitted. |
