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FAIR VALUE MEASUREMENTS - Narrative (Detail) - USD ($) | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020 | Dec. 31, 2018 | Jul. 20, 2018
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Purchase of additional Sangamo France shares | $ 119,000 | $ 503,000 |  |  |
Sangamo France | Share purchase agreement and tender offer agreement |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Number of free shares held by the holders (in shares) |  |  |  | 477,000 | 477,000
Number of ordinary shares acquired (in shares) | 477,000 |  |  |  |
Purchase of additional Sangamo France shares | $ 1,100,000 |  |  |  |
Number of free shares outstanding subject to purchase (in shares) | 0 |  |  |  |
Fair value of free shares' asset | $ 0 |  | $ 0 |  |

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