Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Line Items]
Income tax expense (benefit)	$ 73	$ 68	$ 248	$ 192
Cerus Europe B.V.
Income Tax Disclosure [Line Items]
Income tax expense (benefit)	$ 100	$ 100	$ 200	$ 200