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ACQUISITION OF SANGAMO THERAPEUTICS FRANCE S.A.S. - Narrative (Detail) - USD ($) |  | 2 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Oct. 01, 2018 | Nov. 23, 2018 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Jul. 20, 2018
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Goodwill impairments |  |  | $ 0 | $ 0 |  |  |  |
Sangamo France | Share Purchase Agreement and Tender Offer Agreement |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Noncontrolling interest ownership percentage |  |  | 99.40% |  |  | 98.70% |  |
Sangamo France |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Number of ordinary shares acquired (in shares) | 13,519,036 | 11,528,635 |  |  |  |  |  |
Business acquisition, percentage of voting interests acquired |  |  |  |  |  |  | 98.20% |
Consideration transferred | $ 45,900,000 |  |  |  |  |  |  |
Business acquisition, share price (in dollars per share) | $ 2.99 |  |  |  |  |  |  |
Sangamo France | Share Purchase Agreement and Tender Offer Agreement |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of equity interests agreed to acquire |  |  |  |  |  |  |  | 100.00%
Number of ordinary shares acquired (in shares) |  |  | 228,000 |  | 25,047,671 | 111,000 |  |
Number of free shares held by the holders (in shares) |  |  |  |  |  |  |  | 477,000
Cash paid for shares acquired |  |  | $ 500,000 |  |  |  |  |
Estimated fair value liability of free shares |  |  |  |  |  | $ 200,000 |  | $ 200,000
Estimated fair value asset of free shares |  |  | $ 100,000 |  |  |  |  |
Sangamo France | Share Purchase Agreement and Tender Offer Agreement | Executive Officer |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Number of ordinary shares acquired (in shares) |  |  | 132,700 |  |  |  |  |
Sangamo France | Share Purchase Agreement and Tender Offer Agreement | Option Pricing Method |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated fair value liability of free shares | $ 200,000 |  |  |  |  |  |  |

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