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Acquisition of Sangamo France - Additional Information (Detail) - USD ($)
2 Months Ended 3 Months Ended 12 Months Ended
Oct. 01, 2018
Nov. 23, 2018
Sep. 30, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jul. 20, 2018
Business Acquisition [Line Items]              
Payments to acquire additional interest in subsidiaries       $ 262,000 $ 0 $ 0  
Goodwill impairments       $ 0 $ 0    
TxCell S.A.              
Business Acquisition [Line Items]              
Number of ordinary shares acquired (in shares) 13,519,036 11,528,635          
Percentage of share capital and voting rights acquired         98.20%    
Purchase price per share (in dollars per share) $ 2.99            
Number of shares not purchased by the acquirer 11,981,867            
TxCell S.A. | SPA and TOA              
Business Acquisition [Line Items]              
Percentage of equity interests agreed to acquire             100.00%
Number of ordinary shares acquired (in shares)       111,000 25,047,671    
Number of free shares held by the holders (in shares)             477,000
Payments to acquire additional interest in subsidiaries       $ 300,000      
Business acquisition estimated fair value liabilities of free shares             $ 200,000
Business acquisition estimated fair value assets of free shares       200,000      
TxCell S.A. | SPA and TOA | Option Pricing Method              
Business Acquisition [Line Items]              
Business acquisition estimated fair value liabilities of free shares         $ 200,000    
TxCell S.A. | SPA and TOA | Former Executive of TxCell              
Business Acquisition [Line Items]              
Number of ordinary shares acquired (in shares)     52,700        
Payments to acquire additional interest in subsidiaries       $ 100,000      
TxCell S.A. | SPA              
Business Acquisition [Line Items]              
Number of ordinary shares acquired (in shares) 13,519,036            
TxCell S.A. | SPA and TOA              
Business Acquisition [Line Items]              
Noncontrolling interest, ownership percentage by parent       98.70%