Significant Agreements (Details) - USD ($)			1 Months Ended	12 Months Ended
Significant Agreements (Details) - USD ($)	Jan. 31, 2025	Mar. 25, 2021	Nov. 30, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2021	Oct. 31, 2024	Oct. 31, 2021	Sep. 30, 2021	Aug. 31, 2021	Aug. 09, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development				$ 238,055,000	$ 355,886,000
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
One-time payment							$ 31,000,000.0
Aggregate milestone payments		$ 10,000,000.0
Aggregate milestone payments, period		10 years
Termination period		9 months
Probable milestone payments				0	0
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Development and Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments		$ 100,500,000
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Commercial Sales Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments		$ 390,000,000.0
Affibody \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments								$ 22,000,000.0	$ 3,000,000.0	$ 3,000,000.0
Maximum aggregate milestone payments											$ 280,000,000.0
Aggregate milestone payments, period		10 years
Probable milestone payments				$ 0	$ 0
Payment due prior to milestone											$ 30,000,000.0
Research and development			$ 15,000,000.0			$ 25,000,000.0
Contingent payments, percentage											33.33%
Fair value threshold percentage											33.33%
Affibody \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Subsequent Event
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Notice of termination	90 days

ACELYRIN, Inc. 10-K