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Financial Instruments and Credit Risk - Carrying Amount and Estimated Fair Value of Financial Instruments (Detail) (Fair Value, Measurements, Recurring [Member], USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Quoted Prices in Active Markets (Level 1) [Member]
    
Assets-    
Marketable securities $ 6,175us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 $ 7,230us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Significant Other Observable Inputs (Level 2) [Member]
    
Assets-    
Marketable securities     
Significant Unobservable Inputs (Level 3) [Member]
    
Assets-    
Marketable securities     
Carrying Amount [Member]
    
Assets-    
Marketable securities $ 6,175us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 $ 7,230us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember