Fair Value Measurements (Details 2) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Assets:
Commodity swaps, collars, call options and basis swaps	$ 183,609	$ 131,450
Liabilities:
Commodity swaps, collars, call options and basis swaps	0	(13,764)
Bank debt	0	274,000
Subordinated debt	1,787,678	1,686,536
6.375% Senior Subordinated Notes due 2015 [Member] \| Carrying Value [Member]
Liabilities:
Subordinated debt	0	(150,000)
7.5% senior subordinated notes due 2016, net of discount [Member] \| Carrying Value [Member]
Liabilities:
Subordinated debt	0	(249,683)
7.5% Senior Subordinated Notes due 2017 [Member] \| Carrying Value [Member]
Liabilities:
Subordinated debt	(250,000)	(250,000)
7.25% Senior Subordinated Notes due 2018 [Member] \| Carrying Value [Member]
Liabilities:
Subordinated debt	(250,000)	(250,000)
8.0% senior subordinated notes due 2019, net of discount [Member] \| Carrying Value [Member]
Liabilities:
Subordinated debt	(287,678)	(286,853)
6.75% Senior Subordinated Notes due 2020 [Member] \| Carrying Value [Member]
Liabilities:
Subordinated debt	(500,000)	(500,000)
Carrying Value [Member]
Assets:
Commodity swaps, collars, call options and basis swaps	183,609	123,255
Commodity collars - discontinued operations	0	8,195
Marketable securities	49,199	47,794
Liabilities:
Commodity swaps, collars, call options and basis swaps	0	(13,764)
Carrying Value [Member] \| Bank credit facility [Member]
Liabilities:
Bank debt	0	(274,000)
Carrying Value [Member] \| 5.75% Senior Subordinated Notes due 2021 [Member]
Liabilities:
Subordinated debt	(500,000)	0
6.375% Senior Subordinated Notes due 2015 [Member] \| Fair Value [Member]
Liabilities:
Subordinated debt	0	(153,000)
7.5% senior subordinated notes due 2016, net of discount [Member] \| Fair Value [Member]
Liabilities:
Subordinated debt	0	(259,375)
7.5% Senior Subordinated Notes due 2017 [Member] \| Fair Value [Member]
Liabilities:
Subordinated debt	(265,000)	(263,438)
7.25% Senior Subordinated Notes due 2018 [Member] \| Fair Value [Member]
Liabilities:
Subordinated debt	(266,250)	(263,750)
8.0% senior subordinated notes due 2019, net of discount [Member] \| Fair Value [Member]
Liabilities:
Subordinated debt	(328,500)	(326,625)
6.75% Senior Subordinated Notes due 2020 [Member] \| Fair Value [Member]
Liabilities:
Subordinated debt	(532,500)	(515,625)
Fair Value [Member]
Assets:
Commodity swaps, collars, call options and basis swaps	183,609	123,255
Commodity collars - discontinued operations	0	8,195
Marketable securities	49,199	47,794
Liabilities:
Commodity swaps, collars, call options and basis swaps	0	(13,764)
Fair Value [Member] \| Bank credit facility [Member]
Liabilities:
Bank debt	0	(274,000)
Fair Value [Member] \| 5.75% Senior Subordinated Notes due 2021 [Member]
Liabilities:
Subordinated debt	(518,750)	0
6.375% Senior Subordinated Notes due 2015 [Member]
Liabilities:
Subordinated debt	0	150,000
7.5% senior subordinated notes due 2016, net of discount [Member]
Liabilities:
Subordinated debt	0	249,683
7.5% Senior Subordinated Notes due 2017 [Member]
Liabilities:
Subordinated debt	250,000	250,000
7.25% Senior Subordinated Notes due 2018 [Member]
Liabilities:
Subordinated debt	250,000	250,000
8.0% senior subordinated notes due 2019, net of discount [Member]
Liabilities:
Subordinated debt	287,678	286,853
6.75% Senior Subordinated Notes due 2020 [Member]
Liabilities:
Subordinated debt	$ 500,000	$ 500,000

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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- Definition

The carrying value as of the balance sheet date of the noncurrent portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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