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COLLABORATIONS - Additional Information (Detail) $ in Thousands		1 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 21, 2023 performance_obligation	Jun. 30, 2026 USD ($)	Mar. 31, 2025 USD ($)	Jun. 30, 2024 USD ($) performance_obligation	Sep. 30, 2026 USD ($)	Sep. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Sep. 30, 2026 USD ($) program	Sep. 30, 2025 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2025 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability revenue recognized					$ 4,000	$ 12,500		$ 4,800	$ 53,600
Research and development					408,538	358,814		$ 1,186,538	947,557
Number of separate programs \| program								12
Deferred revenue					11,669			$ 11,669			$ 4,845
Total revenues					1,458,086	1,249,026		3,916,209	2,616,904
Collaborations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues					71,476	351,742		200,716	512,423
Roche \| License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price					1,740,000			1,740,000
Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues					32,334	22,542		83,690	106,123
Regeneron Pharmaceuticals \| Research Services Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue					11,700			$ 11,700			$ 4,800
Vir Biotechnology, Inc. \| Collaborations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues			$ 30,000				$ 30,000
Inceptive Nucleics, Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, initial research term		3 years
Collaboration agreement, right to terminate, written advance notice period		30 days
Purchase price		$ 15,000
Roche Collaboration and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development costs, percentage responsible	40.00%
Profit and loss sharing percentage	50.00%
Number of performance obligations \| performance_obligation	3
Roche Collaboration and License Agreement \| Roche
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development costs, percentage responsible	60.00%
Profit and loss sharing percentage	50.00%
Actual reimbursement of transactional price (as percent)								60.00%
Transaction price					1,738,167			$ 1,738,167
Remaining performance obligation					792,200			792,200
Research and development					66,500	44,800		201,000	105,600
Total revenues					39,107	326,604		116,636	361,927
Global Strategic Collaboration \| Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of performance obligations \| performance_obligation				2
Remaining performance obligation					20,900			20,900
Research and development					9,800	14,600		33,000	46,100
Upfront payment				$ 10,000
Maximum royalties and commercial milestone payments upon potential product sale				$ 325,000
Designated candidates, period after expiration of initial research term				2 years
Maximum additional milestone payments to be receive upon achievement of certain criteria										$ 100,000
Maximum percentage of royalty payments										20.00%
Global Strategic Collaboration \| Regeneron Pharmaceuticals \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement milestone payments, per collaboration project										$ 150,000
Royalty rate										20.00%
Global Strategic Collaboration \| Regeneron Pharmaceuticals \| Funding At Program Initiation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement										$ 2,500
Global Strategic Collaboration \| Regeneron Pharmaceuticals \| Funding At Lead Candidate Identification
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement										$ 2,500
Global Strategic Collaboration \| Regeneron Pharmaceuticals \| C5 Monotherapy Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fixed consideration				$ 191,500
Global Strategic Collaboration \| Regeneron Pharmaceuticals \| Research Services Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price					100,500			100,500
Total revenues					$ 7,345	$ 12,540		$ 13,176	$ 39,306