Development and License Agreements - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		6 Months Ended
	Jul. 31, 2025	Sep. 30, 2022	Jun. 30, 2026	Dec. 31, 2025	Sep. 30, 2024	Sep. 30, 2023
BARDA Agreement
Licenses Agreements [Line Items]
Additional committed fund receivable						$ 3.5
Committed fund receivable			$ 185.2			$ 185.5
Receivable of billed and unbilled amounts			2.5	$ 2.5
2024 BARDA Agreement
Licenses Agreements [Line Items]
Committed fund receivable					$ 32.1
Committed fund receivable			188.4		$ 188.4
2024 BARDA Agreement \| Accounts Receivable, Net
Licenses Agreements [Line Items]
Receivable of billed and unbilled amounts			0.7	0.6
2024 BARDA Agreement \| Cerus Corporation \| Maximum
Licenses Agreements [Line Items]
Co-investment by the company			60.1
DoD and IBAS Program Agreement \| Prepaid and Other Current Assets
Licenses Agreements [Line Items]
Receivable of billed and unbilled amounts			$ 1.4	$ 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