Reconciliation of Numerator and Denominator Used in Computation of Basic and Diluted Net Income Loss per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator for Basic and Diluted:
Net loss attributable to Cerus Corporation	$ (54,374)	$ (59,857)	$ (71,244)
Denominator:
Basic weighted average number of shares outstanding	171,279	163,949	139,831
Diluted weighted average number of shares outstanding	171,279	163,949	139,831
Net loss per share attributable to Cerus Corporation
Basic and diluted	$ (0.32)	$ (0.37)	$ (0.51)