NET REVENUES FROM COLLABORATIONS - Revenue from Collaborators (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	$ 99,476	$ 33,294
Net revenues from collaborations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	27,538	7,003
Net revenues from collaborations | Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	19,503	0
Net revenues from collaborations | Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	6,516	928
Net revenues from collaborations | The Medicines Company
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	1,060	1,745
Net revenues from collaborations | Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	0	4,117
Net revenues from collaborations | Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	$ 459	$ 213