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Stock Option Plans - Additional Information (Detail) (USD $) | 12 Months Ended | 0 Months Ended |
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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 | $ 885,000 us-gaap_AllocatedShareBasedCompensationExpense | $ 622,000 us-gaap_AllocatedShareBasedCompensationExpense | $ 529,000 us-gaap_AllocatedShareBasedCompensationExpense |  |
Number of Shares, Options expected to vest | 859,690 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber |  |  |  |
Number of Shares, Granted | 1,138,170 us-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 |  |  |  |  | 1,275,211 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = ceru_TwoThousandSevenStockIncentivePlanMember
Stock options vesting period | 4 years |  |  |  |
Stock options expiration period | 10 years |  |  |  |
Shares available for future grant | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = ceru_TwoThousandSevenStockIncentivePlanMember | 139,076 us-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 | 1,434,928 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember |  |  |  |
Total intrinsic value of stock options exercised | 161,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | 15,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember |  |
Weighted-average per share grant date fair value of options granted | $ 3.33 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | $ 2.90 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | $ 2.61 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember |  |
Stock-based compensation expense | 885,000 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | 622,000 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | 529,000 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember |  |
Unrecognized compensation cost related to unvested stock-based compensation arrangements | 2,200,000 us-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 | 16,000 us-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 |  | 53,489 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_ChiefExecutiveOfficerMember | 56,053 us-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 |  |  | 60,934 us-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 | $ 56,000 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = ceru_NonEmployeeAwardsMember / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | $ 85,000 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = ceru_NonEmployeeAwardsMember / us-gaap_PlanNameAxis = ceru_TwoThousandFourteenStockIncentivePlanMember | $ 39,000 us-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 | 500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = ceru_TwoThousandAndFourteenEmployeeStockPurchasePlanMember |  |  |  |
Shares issued under Employee Stock Purchase Plan during the period | 0 us-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 |  |  |  | 600,000 us-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 |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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