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Stock Option Plans - Additional Information (Detail) (USD $)
12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jan. 01, 2015
Jan. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock-based compensation expense $ 885,000us-gaap_AllocatedShareBasedCompensationExpense $ 622,000us-gaap_AllocatedShareBasedCompensationExpense $ 529,000us-gaap_AllocatedShareBasedCompensationExpense    
Number of Shares, Options expected to vest 859,690us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber        
Number of Shares, Granted 1,138,170us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross        
2007 Stock Incentive Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Maximum shares of common stock provided under stock incentive plan         1,275,211us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ceru_TwoThousandSevenStockIncentivePlanMember
Stock options vesting period 4 years        
Stock options expiration period 10 years        
Shares available for future grant 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= ceru_TwoThousandSevenStockIncentivePlanMember
139,076us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= ceru_TwoThousandSevenStockIncentivePlanMember
     
2014 Stock Incentive Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock options vesting period 3 years        
Shares available for future grant 1,434,928us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
       
Total intrinsic value of stock options exercised 161,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
15,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
   
Weighted-average per share grant date fair value of options granted $ 3.33us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
$ 2.90us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
$ 2.61us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
   
Stock-based compensation expense 885,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
622,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
529,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
   
Unrecognized compensation cost related to unvested stock-based compensation arrangements 2,200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
       
Weighted-average period of recognition of unrecognized compensation cost related to unvested stock-based compensation arrangements 3 years 7 days        
Number of Shares, Options expected to vest 16,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
       
2014 Stock Incentive Plan [Member] | CEO [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of Shares, Granted   53,489us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
56,053us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
   
2014 Stock Incentive Plan [Member] | Second Company Officer [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of Shares, Granted     60,934us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= ceru_SecondCompanyOfficerMember
   
2014 Stock Incentive Plan [Member] | Non Employee Awards [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock-based compensation expense $ 56,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= ceru_NonEmployeeAwardsMember
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
$ 85,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= ceru_NonEmployeeAwardsMember
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
$ 39,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= ceru_NonEmployeeAwardsMember
/ us-gaap_PlanNameAxis
= ceru_TwoThousandFourteenStockIncentivePlanMember
   
2014 Employee Stock Purchase Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Maximum shares of common stock provided under stock incentive plan 500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ceru_TwoThousandAndFourteenEmployeeStockPurchasePlanMember
       
Shares issued under Employee Stock Purchase Plan during the period 0us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
/ us-gaap_PlanNameAxis
= ceru_TwoThousandAndFourteenEmployeeStockPurchasePlanMember
       
2014 Employee Stock Purchase Plan [Member] | Subsequent Event          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Maximum shares of common stock provided under stock incentive plan       600,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ceru_TwoThousandAndFourteenEmployeeStockPurchasePlanMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
 
Percentage of common stock outstanding stock on first day of the year       1.00%ceru_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockReservedForGrant
/ us-gaap_PlanNameAxis
= ceru_TwoThousandAndFourteenEmployeeStockPurchasePlanMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember