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Stock-Based Compensation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015 Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares of common stock reserved for future issuance	16,900,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Outstanding options and other stock based awards	14,100,000cers_OptionsAndOtherStockBasedAwards
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares of common stock reserved for future issuance	284,130us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_PlanNameAxis = cers_EmployeeStockPurchasePlanMember
Increase in shares of common stock authorized for issuance	1,320,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized / us-gaap_PlanNameAxis = cers_EmployeeStockPurchasePlanMember
Employee Stock Purchase Plan, offering period	12 months
Number of purchase periods within each offering period	2cers_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPurchasePeriod / us-gaap_PlanNameAxis = cers_EmployeeStockPurchasePlanMember
Stock-based compensation, option to be granted at percentage of fair value of common stock	85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_PlanNameAxis = cers_EmployeeStockPurchasePlanMember
2008 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares of common stock reserved for future issuance	2,800,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_PlanNameAxis = cers_TwoThousandEightEquityIncentivePlanMember

X

- Definition

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+ References

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+ Details

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Employee Stock Purchase Plan Offering Term

+ References

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Number Of Purchase Period

+ References

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

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 210.5-02.29)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

+ References

No definition available.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

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