v3.25.4
Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
Jan. 01, 2025
May 23, 2024
Apr. 30, 2021
Dec. 31, 2025
Feb. 29, 2024
Jul. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, terms of award       The 2018 Amended Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, unrestricted stock awards, cash-based awards, and dividend equivalent rights. The 2018 Amended Plan is administered by either the board of directors or the compensation committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the administrator, except that the term of stock options and stock appreciation rights may not be greater than ten years (or five years for certain incentive stock options). Awards typically vest over 12 months to four years. The exercise price for stock options granted may not be less than the fair value of common stock as of the date of grant (or 110% of the fair value of common stock for certain incentive stock options). The fair value of common stock is based on quoted market prices.The 2018 Amended Plan also provides for the assumption of shares remaining available for delivery under the 2019 Stock Plan (as defined below) pursuant to the terms of the Reverse Merger, and such shares will be available for the granting of awards under the 2018 Amended Plan in accordance with applicable stock exchange requirements. The Company also has outstanding stock options under the Magenta Therapeutics, Inc. 2016 Stock Option and Grant Plan, as amended (the “2016 Plan”), but is no longer granting awards under the 2016 Plan.    
Weighted average fair value of stock options granted       $ 18.27    
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross       2,432,800    
Number of shares, options vested and expected to vest       2,336,600    
Additional number of shares reserved and available for issuance 1,555,767          
Warrant [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Common stock exercise price     $ 1.65      
Vesting period       5 years 3 months 18 days    
Warrants issued     4,677      
Warrant per grant date fair value     $ 1.16      
Stock Options and Stock Appreciation Rights [Member] | Maximum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Term of award       10 years    
2018 Stock Option and Incentive Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Total unrecognized stock-based compensation expense related to unvested share-based awards       $ 59.0    
Period for recognition of unrecognized expense       2 years 8 months 12 days    
Number of shares reserved and available for issuance increment percentage   4.00%   5.00%    
2019 Employee Stock Purchase Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, terms of award       The ESPP provides that the number of shares reserved and available for issuance under the ESPP will automatically increase each January 1 through January 1, 2029, by the lesser of (i) 1% of the number of shares issued and outstanding on the immediately preceding December 31, (ii) 62,500 shares and (iii) such number of shares as determined by the Company’s board of directors or its appointed administrator. The number of shares reserved for issuance under the ESPP increased by 62,500 on January 1, 2025.    
Shares available for issuance       143,277    
Percentage of purchase price of common stock under the ESPP       85.00%    
Common stock purchased       18,801    
Additional number of shares reserved and available for issuance 62,500          
2019 Employee Stock Purchase Plan [Member] | Minimum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares reserved and available for issuance increment percentage       1.00%    
Additional number of shares reserved and available for issuance       62,500    
2018 Amended Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares available for issuance       1,174,479    
Percentage of purchase price of common stock under the ESPP       110.00%    
Number of shares reserved and available for issuance increment percentage       5.00%    
Additional number of shares reserved and available for issuance   2,931,820        
2018 Amended Plan [Member] | Stock Options and Stock Appreciation Rights [Member] | Minimum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Vesting period       12 months    
2018 Amended Plan [Member] | Stock Options and Stock Appreciation Rights [Member] | Maximum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Vesting period       4 years    
2018 Amended Plan [Member] | Certain Incentive Stock Options [Member] | Maximum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Term of award       5 years    
2019 Stock Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares, options vested and expected to vest           1,273,454
Inducement Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, number of shares authorized       900,000    
Inducement Plan [Member] | Maximum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, number of shares authorized         300,000  
Amended Inducement Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, number of shares authorized       714,000