v3.25.1
Cover Page - shares
 3 Months Ended
Mar. 31, 2025
May 06, 2025
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2025  
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   55,741,373
Amendment Flag false  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q1  
Entity Central Index Key 0001822462  
Current Fiscal Year End Date --12-31