v3.26.1
Shareholders' Equity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 12 Months Ended
Dec. 31, 2025
Jan. 31, 2025
Oct. 31, 2023
Sep. 30, 2023
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Jun. 30, 2025
Apr. 30, 2025
Sep. 19, 2022
Class of Stock [Line Items]                    
Proceeds from issuance of the Company’s common shares, net of issuance costs paid         $ 0 $ 0 $ 199,822      
Common stock, par value (in dollars per share)         $ 0.0000000341740141 $ 0.0000000341740141        
Investor | Common Shares                    
Class of Stock [Line Items]                    
Stock issued during period (in shares)       19,600,685            
Sale of stock, price (in dollars per share)       $ 10.21            
Net proceeds from sale of common stock       $ 199,800            
Stock Repurchase Program                    
Class of Stock [Line Items]                    
Share repurchase program, authorized, amount               $ 1,500,000    
Share repurchase program, increased authorized, amount         $ 1,000,000          
Share repurchase program, remaining authorized, amount         $ 890,300          
Stock repurchased during period (in shares)         24,225,812 128,361,786        
Stock repurchased during period, value         $ 318,100 $ 1,300,000        
Stock Repurchase Program | Common Shares                    
Class of Stock [Line Items]                    
Stock repurchased during period (in shares)         270,000          
Stock Repurchase Program | Sumitomo Pharma Co. Ltd.                    
Class of Stock [Line Items]                    
Stock repurchased during period (in shares)           71,251,083        
Stock repurchased during period, value           $ 648,400        
Share price (in dollars per share)                 $ 9.10  
Underwritten Public Offering | Immunovant, Inc.                    
Class of Stock [Line Items]                    
Net proceeds from sale of common stock     $ 466,700              
Underwritten Public Offering | Common Shares | Immunovant, Inc.                    
Class of Stock [Line Items]                    
Stock issued during period (in shares)     8,475,500              
Roivant Participation of Immunovant Stock offering | Common Shares                    
Class of Stock [Line Items]                    
Sale of stock, price (in dollars per share)     $ 38.00              
Common shares purchased by RSL (in shares)     1,526,316              
Option purchase additional shares of common stock (in shares)     1,105,500              
Roivant Participation of Immunovant Stock offering | Common Shares | Immunovant, Inc.                    
Class of Stock [Line Items]                    
Common shares purchased by RSL (in shares)   16,845,010                
Proceeds from issuance of the Company’s common shares, net of issuance costs paid   $ 336,900                
Private Placement | Common Shares | Immunovant, Inc.                    
Class of Stock [Line Items]                    
Stock issued during period (in shares)   22,500,000                
Sale of stock, price (in dollars per share)   $ 20.00 $ 38.00              
Common shares purchased by RSL (in shares)     4,473,684              
Proceeds from issuance of the Company’s common shares, net of issuance costs paid   $ 450,000                
Underwritten Offering                    
Class of Stock [Line Items]                    
Sale of stock, number of shares issued in transaction (in shares) 26,200,000                  
Common stock, par value (in dollars per share) $ 21.00                  
Sale of stock, consideration received on transaction $ 543,600                  
Underwritten Offering - Shares Purchased By RSL                    
Class of Stock [Line Items]                    
Sale of stock, number of shares issued in transaction (in shares) 16,666,666                  
Underwritten Offering - Shares Purchased By RSL | Immunovant                    
Class of Stock [Line Items]                    
Equity method investment, ownership percentage 56.00%                  
Cowen | At-the-Market Equity Offering Program                    
Class of Stock [Line Items]                    
Common shares aggregate offering price authorized                   $ 400,000
Common shares aggregate offering price authorized, remaining capacity available         $ 400,000