CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (12,437)	$ (14,139)	$ (45,255)	$ (45,476)
Other comprehensive (loss) income
Unrealized (losses) gains on available-for-sale investments, net of taxes	(136)	(218)	(493)	793
Comprehensive loss	(12,573)	(14,357)	(45,748)	(44,683)
Total comprehensive loss attributable to Cerus Corporation	$ (12,573)	$ (14,357)	$ (45,748)	$ (44,683)