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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
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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 |

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