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