Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets
Commodity swaps, collars, call and put options	$ 348,986	$ 251,500
Liabilities
Derivative Liabilities - Commodity swaps, collars, call and put options	(5,688)	(173)
Bank debt	(235,000)	(187,000)
Subordinated debt	(2,388,562)	(1,787,967)
Carrying Value [Member]
Assets
Commodity swaps, collars, call and put options	348,986	251,500
Marketable securities	56,345	50,237
Liabilities
Derivative Liabilities - Commodity swaps, collars, call and put options	(5,688)	(173)
Bank debt	(235,000)	(187,000)
Fair Value [Member]
Assets
Commodity swaps, collars, call and put options	348,986	251,500
Marketable securities	56,345	50,237
Liabilities
Derivative Liabilities - Commodity swaps, collars, call and put options	(5,688)	(173)
Bank debt	(235,000)	(187,000)
5.75% Senior Subordinated Notes due 2021 [Member] \| Carrying Value [Member]
Liabilities
Subordinated debt	(500,000)	(500,000)
5.75% Senior Subordinated Notes due 2021 [Member] \| Fair Value [Member]
Liabilities
Subordinated debt	(522,500)	(541,250)
7.50% Senior Subordinated Notes due 2017 [Member] \| Carrying Value [Member]
Liabilities
Subordinated debt	(250,000)	(250,000)
7.50% Senior Subordinated Notes due 2017 [Member] \| Fair Value [Member]
Liabilities
Subordinated debt	(261,250)	(265,625)
7.25% Senior Subordinated notes due 2018 [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)
7.25% Senior Subordinated notes due 2018 [Member] \| Fair Value [Member]
Liabilities
Subordinated debt	(265,000)	(267,500)
8.00% Senior Subordinated notes due 2019 [Member]
Liabilities
Subordinated debt	(288,562)	(287,967)
8.00% Senior Subordinated notes due 2019 [Member] \| Carrying Value [Member]
Liabilities
Subordinated debt	(288,562)	(287,967)
8.00% Senior Subordinated notes due 2019 [Member] \| Fair Value [Member]
Liabilities
Subordinated debt	(327,750)	(334,500)
6.75% Senior Subordinated notes due 2020 [Member]
Liabilities
Subordinated debt	(500,000)	(500,000)
6.75% Senior Subordinated notes due 2020 [Member] \| Carrying Value [Member]
Liabilities
Subordinated debt	(500,000)	(500,000)
6.75% Senior Subordinated notes due 2020 [Member] \| Fair Value [Member]
Liabilities
Subordinated debt	(542,500)	(555,000)
5.00% Senior Subordinated notes due 2022 [Member]
Liabilities
Subordinated debt	(600,000)
5.00% Senior Subordinated notes due 2022 [Member] \| Carrying Value [Member]
Liabilities
Subordinated debt	(600,000)
5.00% Senior Subordinated notes due 2022 [Member] \| Fair Value [Member]
Liabilities
Subordinated debt	$ (592,500)

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.

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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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- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

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