NET REVENUES FROM COLLABORATIONS - Additional Information (Detail)			1 Months Ended				9 Months Ended	89 Months Ended
	Sep. 30, 2020 USD ($) candidate	Apr. 08, 2019 USD ($) program	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) shares	Oct. 31, 2017 USD ($) shares	Feb. 28, 2013 USD ($)	Sep. 30, 2020 USD ($) candidate	Jun. 30, 2020 USD ($)
Vir Biotechnology (Vir)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee received					$ 10,000,000.0
Shares of Vir common stock (in shares) | shares					1,111,111
Milestone payment earned			$ 10,000,000.0	$ 15,000,000.0
Milestone shares earned (in shares) | shares				1,111,111
Agreement termination period							90 days
Additional development candidates to be delivered | candidate	4						4
Transaction price	$ 145,200,000
Transactional price remaining performance obligation	96,800,000						$ 96,800,000
Global Strategic Collaboration | Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee received		$ 400,000,000.0
Agreement termination period		90 days
Transaction price	555,100,000						521,600,000
Transactional price remaining performance obligation	$ 254,800,000						$ 254,800,000
Discovery period of programs development		5 years
Extended additional discovery period of programs development		2 years
Maximum royalties and commercial milestone payments upon potential product sale		$ 325,000,000.0
Maximum additional milestone payments to be receive upon achievement of certain criteria		$ 200,000,000.0
Number of targeted programs | program		30
Maximum percentage of royalty payments		20.00%
Global Strategic Collaboration | Funding At Program Initiation | Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement		$ 2,500,000
Global Strategic Collaboration | Funding At Lead Candidate Identification | Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement		2,500,000
Global Strategic Collaboration | Funding At Steady State | Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement		30,000,000.0
Global Strategic Collaboration | Maximum | Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research term extension fee		400,000,000.0
Collaborative arrangement milestone payments		$ 150,000,000.0
Royalty rate		20.00%
Product Alliances [Member] | MDCO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee received						$ 25,000,000.0
Milestone payment earned								$ 30,000,000.0
Maximum amount of potential future milestones						150,000,000.0
Future payments on achievement of specified regulatory milestones						50,000,000.0
Future payments on achievement of specified commercialization milestones						$ 100,000,000.0
Product Alliances [Member] | Minimum | MDCO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate	10.00%						10.00%
Product Alliances [Member] | Maximum | MDCO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate	20.00%						20.00%