Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2021	Sep. 30, 2021 USD ($) Customer Segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Net cash used in operating activities		$ (32,700,000)	$ (32,910,000)
Description of payment of customer invoice contract		The Company invoices its customers based upon the terms in the contracts, which generally requires payment 30 to 60 days from the date of invoice.
Product revenue recognized, that were included in deferred product revenue		$ 500,000
Application of an optional exemption not to disclose the value of unsatisfied performance obligations		true
Number of major customers representing outstanding accounts receivable | Customer		3		3
Inventory valuation reserves		$ 100,000
Number of reportable segments | Segment		1
Period of warranty		1 year
Warranty claim liability		$ 0		$ 0
Cerus Zhongbaokang Shandong Biomedical Co L T D | China
Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, Purpose of VIE		the Company entered into an Equity Joint Venture Contract with Shandong Zhongbaokang Medical Implements Co., Ltd. (“ZBK”), to establish Cerus Zhongbaokang (Shandong) Biomedical Co., LTD. (the “JV”) for the purpose of developing, obtaining regulatory approval for, and eventual manufacturing and commercialization of the INTERCEPT blood transfusion for platelets and red blood cells in the People’s Republic of China.
Ownership percentage	51.00%
Noncontrolling interest in variable interest entity		$ 1,000,000.0
Trade Accounts Receivable | Customer Concentration Risk | Customers
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		61.00%		51.00%
Other Assets
Summary Of Significant Accounting Policies [Line Items]
Cash surrender value of associated life insurance policies		$ 1,000,000.0		$ 200,000
Other Long-term Liabilities
Summary Of Significant Accounting Policies [Line Items]
Liability for deferred compensation		$ 1,100,000		200,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Payment of customer invoice contract period		30 days
Shelf lives of inventory		18 months
Estimated useful life of property and equipment		3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Payment of customer invoice contract period		60 days
Percentage of deferred compensation from base salary		80.00%
Percentage of deferred compensation from variable compensation		100.00%
Shelf lives of inventory		24 months
Inventory valuation reserves				100,000
Estimated useful life of property and equipment		5 years
Product
Summary Of Significant Accounting Policies [Line Items]
Contract asset		$ 0		$ 0
Immaterial Correction of an Error
Summary Of Significant Accounting Policies [Line Items]
Net cash used in operating activities			$ 600,000