MAJOR CUSTOMERS, PARTNERSHIPS AND STRATEGIC ALLIANCES - Novartis Institutes for BioMedical Research, Inc. (Detail) - Novartis Institutes for BioMedical Research, Inc. - Collaboration And License Agreement - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 27, 2020	Aug. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from collaborators		$ 75,000,000					$ 75,000,000
Collaborative arrangement transaction price	$ 95,100,000
License fee	75,000,000
Collaborative arrangement estimated reimbursable service costs	20,100,000
Deferred revenue			$ 48,000,000		$ 48,000,000		70,900,000
Financial advisory fees							$ 1,500,000
Percent of initial recognition							2.00%
Amortization			$ 200,000	$ 0	$ 500,000	$ 0
Achievement Of Specified Preclinical Development Clinical Development And First Commercial Sale Milestones
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received	420,000,000
Achievement Of Commercial Milestones
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received	$ 300,000,000