ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 28,563,000	$ 57,763,000	$ 82,715,000	$ 92,392,000
Net loss	$ (47,688,000)	$ (1,508,000)	$ (140,801,000)	$ (80,447,000)
Earnings per share, basic (in dollars per share)	$ (0.33)	$ (0.01)	$ (0.98)	$ (0.61)
Earnings per share, diluted (in dollars per share)	$ (0.33)	$ (0.01)	$ (0.98)	$ (0.61)
Impairment of goodwill or indefinite-lived intangible assets			$ 0
Impairment of long-lived assets			0
Letter of credit established as a deposit	$ 1,500,000		1,500,000
Sanofi S.A.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	(759,000)	$ 1,498,000	1,258,000	$ 3,789,000
Sanofi S.A. | Change in collaboration agreement scope | Collaboration agreement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	2,500,000		2,500,000
Net loss	$ 2,500,000		$ 2,500,000
Earnings per share, basic (in dollars per share)	$ 0.02	$ 0.02
Earnings per share, diluted (in dollars per share)			$ 0.02	$ 0.02
Pfizer SB-525
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 0		$ 0
Pfizer SB-525 | Change in collaboration agreement scope | Collaboration agreement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 5,800,000		$ 8,900,000
Net loss		$ 5,800,000		$ 8,900,000
Earnings per share, basic (in dollars per share)		$ 0.04		$ 0.06