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Inventory - Schedule of Inventory (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Inventory Disclosure [Abstract]    
Equipment and materials $ 14,219us-gaap_OtherInventorySupplies $ 14,225us-gaap_OtherInventorySupplies
Crude oil inventory 7,737us-gaap_EnergyRelatedInventoryPetroleum 7,129us-gaap_EnergyRelatedInventoryPetroleum
Total inventory $ 21,956us-gaap_InventoryNet $ 21,354us-gaap_InventoryNet