Discontinued Operations (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Revenues and other income
Natural gas, NGL and oil sales	$ 256,687	$ 173,153	$ 483,568	$ 360,826
Transportation and gathering	(1,041)	663	(728)	2,744
Gain on the sale of assets	(1,621)	10,176	(1,482)	78,089
Other	(435)	637	642	(938)
Total revenues and other income	306,629	191,175	494,205	489,600
Costs and expenses
Direct operating	28,509	21,171	57,226	43,007
Production and ad valorem taxes	7,550	5,663	14,429	12,205
Exploration	11,592	14,420	38,779	28,559
Abandonment and impairment of unproved properties	18,900	9,727	35,437	16,278
Interest expense	31,383	21,271	56,162	42,202
Depletion, depreciation and amortization	78,294	67,813	150,510	132,620
Total costs and expenses	228,150	161,766	469,054	333,473
Income tax expense (benefit)
Current	8		8
Deferred	32,695	11,763	12,798	60,775
Total income tax expense (benefit)	32,703	11,763	12,806	60,775
Net income (loss) from discontinued operations	5,517	(8,594)	13,915	(8,721)
Discontinued operations [Member]
Revenues and other income
Natural gas, NGL and oil sales	10,777	33,631	53,034	82,718
Transportation and gathering	1	11	6	23
Gain on the sale of assets	3,820		3,820	955
Other			4
Total revenues and other income	14,598	33,642	56,864	83,696
Costs and expenses
Direct operating	2,169	8,604	10,446	17,808
Production and ad valorem taxes	184	2,427	1,250	3,955
Exploration	5	53	37	549
Abandonment and impairment of unproved properties		3,770		9,626
Interest expense	3,715	9,508	14,791	18,864
Depletion, depreciation and amortization	14	23,184	8,894	47,003
Total costs and expenses	6,087	47,546	35,418	97,805
Income (loss) from discontinued operations before income taxes	8,511	(13,904)	21,446	(14,109)
Income tax expense (benefit)
Current	0	0	0	0
Deferred	2,994	(5,310)	7,531	(5,388)
Total income tax expense (benefit)	2,994	(5,310)	7,531	(5,388)
Net income (loss) from discontinued operations	$ 5,517	$ (8,594)	$ 13,915	$ (8,721)