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Commitments and Contingencies (Details) $ in Thousands			1 Months Ended					3 Months Ended		12 Months Ended
Commitments and Contingencies (Details) $ in Thousands	May 06, 2026 USD ($)	Mar. 01, 2026 USD ($)	Feb. 28, 2026 USD ($) candidate	Dec. 31, 2025 USD ($) asset	Oct. 31, 2025 USD ($)	May 31, 2025 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Aug. 31, 2025 USD ($)	Jul. 31, 2025 USD ($)	May 31, 2023 amendment
Commitments and Contingencies
Purchase obligation								$ 222,900
Research and development								108,692	$ 44,172
Prepaid expenses and other current assets				$ 47,804				64,955
Number of office lease amendment \| amendment														4
Obtaining an operating lease right-of-use asset in exchange for an operating lease liability		$ 1,400				$ 4,000		1,672	$ 0	$ 1,300	$ 1,600
Operating lease right-of-use assets				4,939				6,203
Unrecorded unconditional purchase obligation, including lease not yet commenced, total								$ 9,900
Lessee, operating lease, lease not yet commenced, term of contract								84 months
Operating lease prepayment amount								$ 1,200
Lessee, operating lease, term of contract (in days)		24 months
West Conshohocken, Pennsylvania
Commitments and Contingencies
Operating lease right-of-use assets								4,000
Operating lease, liability								4,600
Faroe License \| Subsequent Event
Commitments and Contingencies
Upfront payment	$ 25,000
Arrowhead License \| Subsequent Event
Commitments and Contingencies
Collaborative arrangement, milestone payment, eligible to receive	$ 975,000
Hoffmann-La Roche ("Roche") \| Research, Development and Commercialization Agreement
Commitments and Contingencies
Milestone payment due							$ 5,000
Remainder of future milestone payments												$ 3,000
CSPC
Commitments and Contingencies
Upfront payment					$ 120,000
Maximum of eligible milestone payments													$ 2,000,000
Pfizer
Commitments and Contingencies
Upfront payment				50,000
Maximum of eligible milestone payments				$ 70,000
Number of additional early stage MASH assets \| asset				2
Suzhou Ribo Life Science Co. Ltd. And Ribocure Pharmaceuticals AB
Commitments and Contingencies
Upfront payment			$ 60,000
Maximum of eligible milestone payments			$ 4,400,000
Number of siRNA candidates \| candidate			6
Research and development								48,300
Prepaid expenses and other current assets								$ 11,700