Debt instrument, available amount upon condition.

No definition available.

Name:	cers_DebtInstrumentAvailableAmountUponCondition
Namespace Prefix:	cers_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt instrument interest only payments date.

+ References

No definition available.

+ Details

Name:	cers_DebtInstrumentInterestOnlyPaymentsDate
Namespace Prefix:	cers_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument principal and declining interest payments additional period.

+ References

No definition available.

+ Details

Name:	cers_DebtInstrumentPrincipalAndDecliningInterestPaymentsAdditionalPeriod
Namespace Prefix:	cers_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt prepayment fee.

+ References

No definition available.

+ Details

Name:	cers_DebtPrepaymentFee
Namespace Prefix:	cers_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Interest only payment period.

+ References

No definition available.

+ Details

Name:	cers_InterestOnlyPaymentPeriod
Namespace Prefix:	cers_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of equal tranches.

+ References

No definition available.

+ Details

Name:	cers_NumberOfEqualTranches
Namespace Prefix:	cers_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Repayments principal and interest aggregate amount.

+ References

No definition available.

+ Details

Name:	cers_RepaymentsPrincipalAndInterestAggregateAmount
Namespace Prefix:	cers_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Trailing net revenue target.

+ References

No definition available.

+ Details

Name:	cers_TrailingNetRevenueTarget
Namespace Prefix:	cers_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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-Section 55
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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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Debt - Additional Information (Detail)		12 Months Ended
Debt - Additional Information (Detail)	Mar. 29, 2019 USD ($) Tranche	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)
Term Loan Credit Agreement
Debt Instrument [Line Items]
Term loan, face amount	$ 70,000,000
Number of loan tranches \| Tranche	3
Debt instrument maturity date	Mar. 01, 2024
Term Loan Credit Agreement \| Two Thousand Nineteen Term Loan
Debt Instrument [Line Items]
Debt instrument floating interest rate percentage	1.80%
Effective interest rate	7.50%
Interest-only payments date	Mar. 01, 2022
Principal plus declining interest payments	24 months
Interest only payment period	12 months
Trailing net revenue target period	12 months
Term Loan Credit Agreement \| Tranche 1
Debt Instrument [Line Items]
Term loan, face amount	$ 40,000,000.0
Term Loan Credit Agreement \| Tranche 2 \| Two Thousand Nineteen Term Loan
Debt Instrument [Line Items]
Term loan, face amount	15,000,000.0
Term Loan Credit Agreement \| Tranche 3 \| Two Thousand Nineteen Term Loan
Debt Instrument [Line Items]
Loan and security agreement available upon revenue achievement	15,000,000.0
Prior Loan Agreement \| 2017 Term Loans
Debt Instrument [Line Items]
Repayments principal and interest aggregate amount	31,200,000
Prepayment fees in aggregate amount	600,000
Prior Loan Agreement \| Interest Expense \| 2017 Term Loans
Debt Instrument [Line Items]
Extinguishment loss recorded		$ 2,100,000
Revolving Loan Credit Agreement
Debt Instrument [Line Items]
Term loan, face amount	5,000,000.0	$ 5,000,000.0	$ 8,500,000
Loan and security agreement available upon revenue achievement	$ 10,000,000.0
Debt instrument floating interest rate percentage	1.80%
Borrowing limit			$ 10,000,000.0
Revolving Loan Credit Agreement \| Two Thousand Nineteen Term Loan
Debt Instrument [Line Items]
Debt instrument maturity date	Mar. 01, 2024