Supplemental Gas Data Capitalized Costs (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proven properties	$ 1,549,773	$ 1,495,772
Unproven properties	1,266,444	1,258,455
Wells and related equipment	2,113,414	1,755,617
Gathering assets	1,006,882	963,494
Total Property, Plant and Equipment	5,936,513	5,473,338
Accumulated Depreciation, Depletion and Amortization	(953,873)	(773,027)
Net Capitalized Costs	$ 4,982,640	$ 4,700,311

Capitalized costs of proved properties incurred for any combination mineral interests acquisitions; wells and related equipment; support equipment and facilities; and uncompleted wells and equipment and other costs not previously disclosed within this table.

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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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- Definition

Capitalized costs of unproved properties incurred for any combination mineral interests acquisitions and other costs not previously disclosed within this table.

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- Definition

Capitalized costs which include those incurred to (1) to drill and equip those exploratory wells and exploratory-type stratigraphic test wells that have found proved reserves and (2) obtain access to proved reserves and provide facilities for extracting, treating, gathering, storing the oil and gas, including the drilling and equipping of development wells and development-type stratigraphic wells and service wells.

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