Subsequent Events - Additional Information (Detail) - Subsequent Event - USD ($)	Jul. 31, 2017	Aug. 04, 2017
Cantor \| Sales Agreement \| Amendment No. 3
Subsequent Event [Line Items]
Common stock registered for sale		$ 70,000,000
Cerus Restated Term Loan Agreement
Subsequent Event [Line Items]
Maximum borrowing limit	$ 40,000,000
Maturity period	Jul. 01, 2022
Final payment term percent	8.00%
Terms of required periodic payments of interest and principal	The Restated Term Loan Agreement provides for secured growth capital loans of up to $40.0 million (the “Term Loans”). All of the Company’s current and future assets, excluding its intellectual property and 35% of the Company’s investment in Cerus Europe B.V., are secured for its borrowings under the Restated Term Loan Agreement. On July 31, 2017, the Company received $30.0 million from the first tranche under the Restated Term Loan Agreement, and settled its prior Term Loan Agreement. The second tranche of $10.0 million will be available subject to the Company achieving consolidated trailing six months’ revenue at a specified threshold no later than January 31, 2019. The Term Loans shall be interest-only through February 1, 2019 followed by 42 months of equal principal and interest.
Borrowing conditions	However, if the Company draws the Term Loan Two, then the interest-only period will be extended through August 1, 2019, and the amortization period will be reduced to 36 months.
Interest rate, description	The interest rate of the term loans is 6.72% plus the index rate, which is floating and will be reset monthly as the greater of (i) 8.01% and (ii) the sum of the three-month U.S. LIBOR rate plus (b) 6.72%. The Company will also be required to make a final payment fee of 8.00% of the amounts of the Term Loans drawn payable on the earlier of (i) the prepayment of the Term Loans or (ii) the Maturity Date.
Cerus Restated Term Loan Agreement \| Three-month U.S. LIBOR
Subsequent Event [Line Items]
Debt, applicable margin	6.72%
Cerus Restated Term Loan Agreement \| Minimum
Subsequent Event [Line Items]
Debt instrument floating interest rate percentage	8.01%
Cerus Restated Term Loan Agreement \| First Tranche (Term Loan A)
Subsequent Event [Line Items]
Loan and security agreement	$ 30,000,000
Interest-only payment date	Feb. 01, 2019
Principal and interest payments	42 months
Cerus Restated Term Loan Agreement \| Second Tranche (Term Loan B)
Subsequent Event [Line Items]
Loan and security agreement available upon revenue achievement	$ 10,000,000
Interest-only period extension date	Aug. 01, 2019
Amortization Period	36 months
Cerus Restated Term Loan Agreement \| Securities Pledged as Collateral
Subsequent Event [Line Items]
Percentage of investments made in subsidiary	35.00%

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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