v3.26.1
Cover Page - shares
 3 Months Ended
Mar. 31, 2026
May 08, 2026
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Entity Central Index Key 0002114044  
Document Quarterly Report true  
Document Transition Report false  
Entity Registrant Name Hemab Therapeutics Holdings, Inc.  
Entity File Number 001-43250  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Current Fiscal Year End Date --12-31  
Entity Tax Identification Number 41-4241952  
Entity Incorporation, State or Country Code DE  
Entity Address, Address Line One 101 Main Street  
Entity Address, Address Line Two Suite 1220  
Entity Address, City or Town Cambridge  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02142  
City Area Code 617  
Local Phone Number 553-3952  
Title of 12(b) Security Common Stock, $0.0001 par value per share  
Trading Symbol COAG  
Security Exchange Name 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   46,705,410