Development and License Agreements - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended			9 Months Ended
	Jul. 31, 2026	Jul. 31, 2025	Sep. 30, 2022	Sep. 30, 2026	Dec. 31, 2025	Sep. 30, 2024	Sep. 30, 2023
BARDA Agreement
Licenses Agreements [Line Items]
Additional committed fund receivable	$ 33.2						$ 3.5
Committed fund receivable	65.3			$ 185.2			$ 185.5
Receivable of billed and unbilled amounts				1.5	$ 2.5
2024 BARDA Agreement
Licenses Agreements [Line Items]
Committed fund receivable						$ 32.1
Committed fund receivable				209.0		$ 188.4
Committed fund receivable	209.0
Committed fund receivable, increased	$ 20.6
2024 BARDA Agreement \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsReceivableNetCurrent
Licenses Agreements [Line Items]
Receivable of billed and unbilled amounts				1.5	0.6
2024 BARDA Agreement \| Cerus Corporation \| Maximum
Licenses Agreements [Line Items]
Co-investment by the company				61.5
DoD and IBAS Program Agreement \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:PrepaidExpenseAndOtherAssetsCurrent
Licenses Agreements [Line Items]
Receivable of billed and unbilled amounts				$ 0.3	$ 0.4
DoD and IBAS Program Agreement \| Maximum
Licenses Agreements [Line Items]
Total contract value		$ 25.0	$ 17.8
DoD and IBAS Program Agreement \| Minimum
Licenses Agreements [Line Items]
Total contract value		$ 7.2	$ 9.1