Discontinued Operations (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenues and other income
Natural gas, NGL and oil sales	$ 271,799	$ 187,757	$ 755,367	$ 548,583
Transportation and gathering	816	(1,640)	88	1,104
Gain on the sale of assets	203	67	(1,280)	78,156
Other	(375)	(1,010)	268	(1,948)
Total revenues and other income	338,205	195,155	832,410	684,755
Costs and expenses
Direct operating	29,828	25,535	87,054	68,542
Production and ad valorem taxes	7,317	6,903	21,746	19,108
Exploration	17,606	15,225	56,385	43,784
Abandonment and impairment of unproved properties	16,627	14,435	52,064	30,713
Interest expense	34,181	23,363	90,343	65,565
Depletion, depreciation and amortization	93,619	69,730	244,129	202,350
Total costs and expenses	282,479	191,718	751,533	525,191
Income tax expense (benefit)
Current	(7)	(10)	1	(10)
Deferred	22,547	794	35,345	61,569
Total income tax expense (benefit)	22,540	784	35,346	61,559
Net income (loss) from discontinued operations	1,569	(10,821)	15,484	(19,542)
Discontinued operations [Member]
Revenues and other income
Natural gas, NGL and oil sales	723	31,803	53,757	114,521
Transportation and gathering		6	6	29
Gain on the sale of assets	1,032		4,852	955
Other		(3)	4	(3)
Total revenues and other income	1,755	31,806	58,619	115,502
Costs and expenses
Direct operating	(611)	8,752	9,835	26,560
Production and ad valorem taxes	(44)	1,970	1,206	5,925
Exploration		11	37	560
Abandonment and impairment of unproved properties		6,099		15,725
Interest expense		10,443	14,791	29,307
Depletion, depreciation and amortization		22,038	8,894	69,041
Total costs and expenses	(655)	49,313	34,763	147,118
Income (loss) from discontinued operations before income taxes	2,410	(17,507)	23,856	(31,616)
Income tax expense (benefit)
Current		0		0
Deferred	841	(6,686)	8,372	(12,074)
Total income tax expense (benefit)	841	(6,686)	8,372	(12,074)
Net income (loss) from discontinued operations	$ 1,569	$ (10,821)	$ 15,484	$ (19,542)