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Stock Based Compensation - Additional Information (Detail) (USD $)
3 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Aug. 31, 2012
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Outstanding options to purchase shares of common stock 64,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber     101,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Stock-based compensation expense $ 143,000us-gaap_ShareBasedCompensation $ 157,000us-gaap_ShareBasedCompensation    
Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested restricted shares outstanding 165,491us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
    268,985us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Unrecognized compensation cost 475,200us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Number of restricted shares vested 103,494us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
[1]      
Intrinsic value of restricted shares vested $ 370,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Common stock cancelled in payment of payroll taxes due on vesting of restricted shares under employee stock incentive plans (in shares) 9,998crv_CommonStockCanceledForPaymentOfPayrollTaxesOnVestingOfShareBasedCompensationShares
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Tax withholding obligations 35,000us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Unrecognized stock-based compensation expense are expected to be recognized over a weighted average periods (years) 1 year 4 months 24 days      
Restricted shares outstanding expected to vest 165,491crv_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Aggregate intrinsic value 571,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueNonvested
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Restricted Stock | Service Contingent | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period 3 years      
Restricted Stock | Service Contingent | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period 4 years      
Restricted Stock | Performance Contingent        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested restricted shares outstanding 165,491us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ crv_StockOptionPlanTypeAxis
= us-gaap_PerformanceSharesMember
     
Unvested Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation cost $ 0us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= crv_UnvestedStockOptionsMember
     
2012 Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares initially authorized for issuance under equity incentive plan     300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanTwentyTwelveMember
 
Additional shares authorized for issuance under equity incentive plan     17,666us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanTwentyTwelveMember
 
Shares redistributed and made available for grant 308,821us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanTwentyTwelveMember
     
Outstanding shares remained available for future grants 419,330us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanTwentyTwelveMember
     
Previously Approved Plans        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares ceased to be issuable     17,666crv_ShareBasedCompensationArrangementByShareBasedPaymentAwardAvailableForGrantCancelledInPeriod
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanMember
 
2012 Plan and Previously Approved Plans        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Outstanding options to purchase shares of common stock 64,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanTwentyTwelveAndPreviouslyApprovedPlansMember
     
2012 Plan and Previously Approved Plans | Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested restricted shares outstanding 165,491us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ crv_IncentiveCompensationPlansEmployeesAxis
= crv_EquityIncentivePlanTwentyTwelveAndPreviouslyApprovedPlansMember
     
[1] Service-based restricted shares.