Condensed Consolidating Financial Statements (Condensed Consolidating Statement Of Cash Flows) (Details) (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Net cash provided by operating activities	$ 355,334	$ 275,996
Additions to oil and natural gas properties, gathering systems and equipment and property acquisitions	(1,491,850)	(888,078)
Proceeds from disposition of property and equipment	428,332	995,573
Investment in equity investments	(13,969)	(100,000)
Return of investment in equity investments	125,000	0
Restricted cash	44,378	(41,340)
Advances (to) from Appalachia JV	3,306	(10,318)
Deposit on pending acquisitions	464,151	0
Other	(5,750)	0
Advances/investments with affiliates	0	0
Net cash used in investing activities	(446,402)	(44,163)
Borrowings under credit agreements	521,000	1,402,399
Repayments under credit agreements	(397,500)	(1,895,563)
Proceeds from issuance of 2018 Notes	0	738,975
Repayment of 2011 Notes	0	(444,720)
Proceeds from issuance of common stock, net	11,776	9,776
Payment of common stock dividends	(25,673)	(21,238)
Payment for common stock repurchased	0	(7,479)
Settlement of derivative financial instruments with a financing element		(907)
Deferred financing costs and other	(6,346)	(30,359)
Net cash provided by (used in) financing activities	103,257	(249,116)
Net increase (decrease) in cash	12,189	(17,283)
Cash at beginning of period	44,229	68,407
Cash at end of period	56,418	51,124
Resources [Member]
Net cash provided by operating activities	61,069	56,229
Additions to oil and natural gas properties, gathering systems and equipment and property acquisitions	(51,201)	(50,366)
Proceeds from disposition of property and equipment	3,128	8,896
Investment in equity investments	0	0
Return of investment in equity investments	0
Restricted cash	0	0
Advances (to) from Appalachia JV	0	0
Deposit on pending acquisitions	0
Other	0
Advances/investments with affiliates	(113,717)	292,494
Net cash used in investing activities	(161,790)	251,024
Borrowings under credit agreements	521,000	1,352,437
Repayments under credit agreements	(397,500)	(1,870,582)
Proceeds from issuance of 2018 Notes		738,975
Repayment of 2011 Notes		(444,720)
Proceeds from issuance of common stock, net	11,776	9,776
Payment of common stock dividends	(25,673)	(21,238)
Payment for common stock repurchased		(7,479)
Settlement of derivative financial instruments with a financing element		(907)
Deferred financing costs and other	(6,346)	(30,359)
Net cash provided by (used in) financing activities	103,257	(274,097)
Net increase (decrease) in cash	2,536	33,156
Cash at beginning of period	76,763	47,412
Cash at end of period	79,299	80,568
Guarantor Subsidiaries [Member]
Net cash provided by operating activities	293,094	228,216
Additions to oil and natural gas properties, gathering systems and equipment and property acquisitions	(1,436,396)	(599,808)
Proceeds from disposition of property and equipment	425,204	986,677
Investment in equity investments	(13,969)	(100,000)
Return of investment in equity investments	125,000
Restricted cash	44,378	(41,340)
Advances (to) from Appalachia JV	3,306	(10,318)
Deposit on pending acquisitions	464,151
Other	(5,750)
Advances/investments with affiliates	110,635	(538,847)
Net cash used in investing activities	(283,441)	(303,636)
Borrowings under credit agreements	0	49,962
Repayments under credit agreements	0	(24,981)
Proceeds from issuance of 2018 Notes		0
Repayment of 2011 Notes		0
Proceeds from issuance of common stock, net	0	0
Payment of common stock dividends	0	0
Payment for common stock repurchased		0
Settlement of derivative financial instruments with a financing element		0
Deferred financing costs and other	0	0
Net cash provided by (used in) financing activities	0	24,981
Net increase (decrease) in cash	9,653	(50,439)
Cash at beginning of period	(32,534)	20,995
Cash at end of period	(22,881)	(29,444)
Non-Guarantor Subsidiaries [Member]
Net cash provided by operating activities	1,171	(8,449)
Additions to oil and natural gas properties, gathering systems and equipment and property acquisitions	(4,253)	(237,904)
Proceeds from disposition of property and equipment	0	0
Investment in equity investments	0	0
Return of investment in equity investments	0
Restricted cash	0	0
Advances (to) from Appalachia JV	0	0
Deposit on pending acquisitions	0
Other	0
Advances/investments with affiliates	3,082	246,353
Net cash used in investing activities	(1,171)	8,449
Borrowings under credit agreements	0	0
Repayments under credit agreements	0	0
Proceeds from issuance of 2018 Notes		0
Repayment of 2011 Notes		0
Proceeds from issuance of common stock, net	0	0
Payment of common stock dividends	0	0
Payment for common stock repurchased		0
Settlement of derivative financial instruments with a financing element		0
Deferred financing costs and other	0	0
Net cash provided by (used in) financing activities	0	0
Net increase (decrease) in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	0	0
Eliminations [Member]
Net cash provided by operating activities	0	0
Additions to oil and natural gas properties, gathering systems and equipment and property acquisitions	0	0
Proceeds from disposition of property and equipment	0	0
Investment in equity investments	0	0
Return of investment in equity investments	0
Restricted cash	0	0
Advances (to) from Appalachia JV	0	0
Deposit on pending acquisitions	0
Other	0
Advances/investments with affiliates	0	0
Net cash used in investing activities	0	0
Borrowings under credit agreements	0	0
Repayments under credit agreements	0	0
Proceeds from issuance of 2018 Notes		0
Repayment of 2011 Notes		0
Proceeds from issuance of common stock, net	0	0
Payment of common stock dividends	0	0
Payment for common stock repurchased		0
Settlement of derivative financial instruments with a financing element		0
Deferred financing costs and other	0	0
Net cash provided by (used in) financing activities	0	0
Net increase (decrease) in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	$ 0	$ 0