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FAIR VALUE MEASUREMENTS - Summary of Estimated Fair Value of Free Shares Valuation Assumptions (Detail)
Dec. 31, 2020
$ / shares
Dec. 31, 2020
€ / shares
Oct. 01, 2018
$ / shares
Stock price      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Sangamo stock price (USD) (in dollars per share) $ 15.61    
Exchange rate      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
EUR / USD exchange rate 0.82 0.82  
Stock price volatility estimate      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Volatility estimate 0.889 0.889  
Price volatility      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Volatility estimate 0.063 0.063  
Sangamo France      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Sangamo France stock price (EUR) (in euros per share)     $ 2.99
Sangamo France | Stock price      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Sangamo France stock price (EUR) (in euros per share) | € / shares   € 3.85  
Sangamo France | Stock price correlation      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Estimated correlation between Sangamo and Sangamo France stock prices 1.000 1.000  
Sangamo France | Stock price volatility estimate      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Volatility estimate 0.889 0.889