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Derivative Financial Instruments and Fair Value Measurements - Summary of Derivative Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Commodities Contracts, USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Derivatives, Fair Value [Line Items]    
Asset, Fair Value $ 2us-gaap_DerivativeAssets $ 969us-gaap_DerivativeAssets
Liability - Fair Value 4,392us-gaap_DerivativeLiabilities 318us-gaap_DerivativeLiabilities
Level 2    
Derivatives, Fair Value [Line Items]    
Asset, Fair Value 2us-gaap_DerivativeAssets
/ us-gaap_DerivativeByNatureAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
969us-gaap_DerivativeAssets
/ us-gaap_DerivativeByNatureAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Liability - Fair Value $ 4,392us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeByNatureAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
$ 318us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeByNatureAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member