ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues from Strategic Partnering Collaboration Agreements and Research Activity Grants (Detail) - Revenue from contract with customer - Customer concentration risk	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Novartis Institutes for BioMedical Research, Inc.
Concentration Risk [Line Items]
Percentage of revenues	40.00%	0.00%	35.00%	0.00%
Biogen MA, Inc.
Concentration Risk [Line Items]
Percentage of revenues	38.00%	16.00%	39.00%	19.00%
Kite Pharma, Inc.
Concentration Risk [Line Items]
Percentage of revenues	22.00%	13.00%	23.00%	24.00%
Sanofi S.A.
Concentration Risk [Line Items]
Percentage of revenues	(3.00%)	3.00%	2.00%	4.00%
Pfizer Inc.
Concentration Risk [Line Items]
Percentage of revenues	0.00%	68.00%	0.00%	51.00%