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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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