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Retirement Plans - Additional Information (Detail) (Safe Harbor Plan [Member], USD $) In Thousands, unless otherwise specified	0 Months Ended	12 Months Ended
	Jan. 01, 2010	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Safe Harbor Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	4.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ceru_SafeharborPlanMember
Defined contribution plan, employer matching contribution		$ 163us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ceru_SafeharborPlanMember	$ 145us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ceru_SafeharborPlanMember	$ 165us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ceru_SafeharborPlanMember

X

- Details

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

X

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

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

X

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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