MAJOR CUSTOMERS, PARTNERSHIPS AND STRATEGIC ALLIANCES - Revenues Recognized under Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	$ 26,280	$ 13,076
Kite Pharma, Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	6,288	7,219
Kite Pharma, Inc. | Recognition of license and stand-ready fee
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	6,159	6,227
Kite Pharma, Inc. | Research services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	129	992
Sanofi
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	1,060	499
Sanofi | Recognition of license and stand-ready fee
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	227	(729)
Sanofi | Research services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	679	1,720
Sanofi | Milestone achievement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	$ 154	$ (492)