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Stock-Based Compensation - Additional Information (Detail) | 3 Months Ended
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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 | 16,900,000 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Outstanding options and other stock based awards | 14,100,000 cers_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 | 284,130 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_PlanNameAxis = cers_EmployeeStockPurchasePlanMember
Increase in shares of common stock authorized for issuance | 1,320,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized / us-gaap_PlanNameAxis = cers_EmployeeStockPurchasePlanMember
Employee Stock Purchase Plan, offering period | 12 months
Number of purchase periods within each offering period | 2 cers_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 | 2,800,000 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_PlanNameAxis = cers_TwoThousandEightEquityIncentivePlanMember

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- Definition Outstanding options and other stock-based awards under equity incentive plans other than the employee stock purchase plan + References No definition available. + Details
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Namespace Prefix: | cers_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Definition Share Based Compensation Arrangement By Share Based Payment Award Employee Stock Purchase Plan Offering Term + References No definition available. + Details
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Namespace Prefix: | cers_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Share Based Compensation Arrangement By Share Based Payment Award Number Of Purchase Period + References No definition available. + Details
Name: | cers_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPurchasePeriod
Namespace Prefix: | cers_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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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 + Details
Name: | us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of additional shares authorized for issuance under an established share-based compensation plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition Purchase price of common stock expressed as a percentage of its fair value. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_PlanNameAxis=cers_EmployeeStockPurchasePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PlanNameAxis=cers_TwoThousandEightEquityIncentivePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |