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Summary of Significant Accounting Policies - Inventory (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Accounting Policies [Abstract]    
Equipment and materials $ 14,225us-gaap_OtherInventorySupplies $ 11,669us-gaap_OtherInventorySupplies
Crude oil inventory 7,129us-gaap_EnergyRelatedInventoryPetroleum 8,983us-gaap_EnergyRelatedInventoryPetroleum
Inventory, net $ 21,354us-gaap_InventoryNet $ 20,652us-gaap_InventoryNet