Capitalized Costs and Accumulated Depreciation Depletion and Amortization (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Natural gas and oil properties:
Properties subject to depletion	$ 5,689,410	$ 4,742,248
Unproved properties	730,620	648,143
Total	6,420,030	5,390,391
Accumulated depreciation, depletion and amortization	(1,573,195)	(1,306,378)
Net capitalized costs	$ 4,846,835	$ 4,084,013

Amount of accumulated depreciation, depletion, amortization and valuation allowance relating to oil and gas producing activities.

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-Name Statement of Financial Accounting Standard (FAS)

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The sum of capitalized costs relating to oil and gas producing activities before accounting for accumulated depreciation.

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Net amount of capitalized costs relating to oil and gas producing activities.

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

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