Condensed Consolidating Financial Statements (Schedule Of Condensed Consolidating Statement Of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net cash provided by operating activities	$ 145,123	$ 79,073
Property acquisitions and additions to oil and natural gas properties, gathering systems and equipment	(171,158)	(706,443)
Deposit on acquisitions	0	464,151
Equity investments	(137)	(162)
Return of investment in equity investments	0	125,000
Proceeds from disposition of property and equipment	981	259,103
Restricted cash	(8,117)	11,125
Net changes in advances (to) from Appalachia JV	10,543	(5,063)
Other	0	(1,250)
Advances/investments with affiliates	0	0
Net cash provided by (used in) investing activities	(167,888)	146,461
Borrowings under credit agreements	53,000	40,000
Repayments under credit agreements	(23,000)	(300,000)
Proceeds from issuance of common stock	2	7,312
Payment of common stock dividends	(8,663)	(8,547)
Net cash provided by (used in) financing activities	21,339	(261,235)
Net decrease in cash	(1,426)	(35,701)
Cash at beginning of period	31,997	44,229
Cash at end of period	30,571	8,528
Resources [Member]
Net cash provided by operating activities	40,676	18,448
Property acquisitions and additions to oil and natural gas properties, gathering systems and equipment	(10,120)	(17,463)
Deposit on acquisitions		0
Equity investments	0	0
Return of investment in equity investments		0
Proceeds from disposition of property and equipment	0	39
Restricted cash	0	0
Net changes in advances (to) from Appalachia JV	0	0
Other		0
Advances/investments with affiliates	(78,910)	233,700
Net cash provided by (used in) investing activities	(89,030)	216,276
Borrowings under credit agreements	53,000	40,000
Repayments under credit agreements	(23,000)	(300,000)
Proceeds from issuance of common stock	2	7,312
Payment of common stock dividends	(8,663)	(8,547)
Net cash provided by (used in) financing activities	21,339	(261,235)
Net decrease in cash	(27,015)	(26,511)
Cash at beginning of period	78,664	76,763
Cash at end of period	51,649	50,252
Guarantor Subsidiaries [Member]
Net cash provided by operating activities	104,447	59,468
Property acquisitions and additions to oil and natural gas properties, gathering systems and equipment	(161,038)	(685,916)
Deposit on acquisitions		464,151
Equity investments	(137)	(162)
Return of investment in equity investments		125,000
Proceeds from disposition of property and equipment	981	259,064
Restricted cash	(8,117)	11,125
Net changes in advances (to) from Appalachia JV	10,543	(5,063)
Other		(1,250)
Advances/investments with affiliates	78,910	(235,607)
Net cash provided by (used in) investing activities	(78,858)	(68,658)
Borrowings under credit agreements	0	0
Repayments under credit agreements	0	0
Proceeds from issuance of common stock	0	0
Payment of common stock dividends	0	0
Net cash provided by (used in) financing activities	0	0
Net decrease in cash	25,589	(9,190)
Cash at beginning of period	(46,667)	(32,534)
Cash at end of period	(21,078)	(41,724)
Non-Guarantor Subsidiaries [Member]
Net cash provided by operating activities	0	1,157
Property acquisitions and additions to oil and natural gas properties, gathering systems and equipment	0	(3,064)
Deposit on acquisitions		0
Equity investments	0	0
Return of investment in equity investments		0
Proceeds from disposition of property and equipment	0	0
Restricted cash	0	0
Net changes in advances (to) from Appalachia JV	0	0
Other		0
Advances/investments with affiliates	0	1,907
Net cash provided by (used in) investing activities	0	(1,157)
Borrowings under credit agreements	0	0
Repayments under credit agreements	0	0
Proceeds from issuance of common stock	0	0
Payment of common stock dividends	0	0
Net cash provided by (used in) financing activities	0	0
Net 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
Property acquisitions and additions to oil and natural gas properties, gathering systems and equipment	0	0
Deposit on acquisitions		0
Equity investments	0	0
Return of investment in equity investments		0
Proceeds from disposition of property and equipment	0	0
Restricted cash	0	0
Net changes in advances (to) from Appalachia JV	0	0
Other		0
Advances/investments with affiliates	0	0
Net cash provided by (used in) investing activities	0	0
Borrowings under credit agreements	0	0
Repayments under credit agreements	0	0
Proceeds from issuance of common stock	0	0
Payment of common stock dividends	0	0
Net cash provided by (used in) financing activities	0	0
Net decrease in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	$ 0	$ 0