Properties and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment
Proved Natural Gas and Crude Oil Properties	$ 2,360,880	$ 2,267,165
Unproved Natural Gas and Crude Oil Properties	188,518	188,206
Total Natural Gas and Crude Oil Properties	2,549,398	2,455,371
Equipment and other	31,217	29,562
Land and Buildings	9,016us-gaap_BuildingsAndImprovementsGross	9,015us-gaap_BuildingsAndImprovementsGross
Construction in Progress	178,804us-gaap_ConstructionInProgressGross	137,937us-gaap_ConstructionInProgressGross
Properties and equipment, at cost	2,768,435us-gaap_PropertyPlantAndEquipmentGross	2,631,885us-gaap_PropertyPlantAndEquipmentGross
Accumulated DD&A	(887,432)	(831,699)
Property, Plant and Equipment, Net	$ 1,881,003us-gaap_PropertyPlantAndEquipmentNet	$ 1,800,186us-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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Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.

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Capitalized costs incurred for support equipment and facilities used in oil and gas producing activities (such as seismic equipment, drilling equipment, construction and grading equipment, vehicles, repair shops, warehouses, supply points, camps, and division, district, or field offices).

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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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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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services 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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Oil and Gas properties with proved reserves under the successful effort method.

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Oil and Gas properties with unproved reserves under the successful effort method.

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