Summary of Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Oil and gas properties:
Proved	$ 3,506,603	$ 2,970,047
Unproved	125,676	101,520
Total oil and gas properties	3,632,279	3,071,567
Other property and equipment	75,073us-gaap_PropertyPlantAndEquipmentOther	105,421us-gaap_PropertyPlantAndEquipmentOther
Total property and equipment	3,707,352us-gaap_PropertyPlantAndEquipmentGross	3,176,988us-gaap_PropertyPlantAndEquipmentGross
Accumulated depreciation, depletion and amortization	(1,882,254)	(939,684)
Property and equipment, net (successful efforts method)	$ 1,825,098us-gaap_PropertyPlantAndEquipmentNet	$ 2,237,304us-gaap_PropertyPlantAndEquipmentNet

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Oil and Gas properties, gross, carried under the successful effort method.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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