Condensed Consolidating Financial Statements (Condensed Consolidating Statement Of Operations) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Oil and natural gas	$ 207,274	$ 130,990	$ 575,330	$ 380,328
Oil and natural gas production	27,754	25,140	79,543	83,222
Gathering and transportation	22,279	11,561	59,069	35,547
Depreciation, depletion and amortization	100,491	53,687	253,833	137,844
Accretion of discount on asset retirement obligations	938	830	2,728	2,920
General and administrative	29,875	24,034	76,435	76,319
(Gain) loss on divestitures and other operating items	21,045	6,257	25,171	(569,096)
Total costs and expenses	202,382	121,509	496,779	(233,244)
Operating income	4,892	9,481	78,551	613,572
Interest expense	(15,090)	(8,440)	(43,585)	(33,550)
Gain on derivative financial instruments	84,284	56,209	130,978	156,065
Other income (expense)	193	67	555	184
Equity income	10,666	6,675	22,749	12,054
Equity in earnings of subsidiaries	0	0	0	0
Total other income (expense)	80,053	54,511	110,697	134,753
Income before income taxes	84,945	63,992	189,248	748,325
Income tax expense (benefit)	0	(904)	0	3,548
Net income	84,945	64,896	189,248	744,777
Resources [Member]
Oil and natural gas	22,725	17,025	70,115	50,747
Oil and natural gas production	4,987	3,833	14,334	11,684
Gathering and transportation	1	0	1	0
Depreciation, depletion and amortization	11,609	8,540	25,379	21,387
Accretion of discount on asset retirement obligations	113	87	321	255
General and administrative	10,059	6,468	19,375	20,725
(Gain) loss on divestitures and other operating items	15,753	5,652	20,355	7,816
Total costs and expenses	42,522	24,580	79,765	61,867
Operating income	(19,797)	(7,555)	(9,650)	(11,120)
Interest expense	(15,089)	(8,439)	(42,326)	(26,814)
Gain on derivative financial instruments	74,063	30,427	113,670	64,369
Other income (expense)	77	16	262	10,345
Equity income	0	0	0	0
Equity in earnings of subsidiaries	45,691	49,543	127,292	711,545
Total other income (expense)	104,742	71,547	198,898	759,445
Income before income taxes	84,945	63,992	189,248	748,325
Income tax expense (benefit)	0	(904)	0	3,548
Net income	84,945	64,896	189,248	744,777
Guarantor Subsidiaries [Member]
Oil and natural gas	184,549	108,362	505,215	320,250
Oil and natural gas production	22,767	20,755	65,209	70,625
Gathering and transportation	22,278	11,254	59,068	34,948
Depreciation, depletion and amortization	88,733	43,071	227,501	113,135
Accretion of discount on asset retirement obligations	825	742	2,407	2,663
General and administrative	19,816	17,566	57,061	55,594
(Gain) loss on divestitures and other operating items	5,568	605	6,098	(576,912)
Total costs and expenses	159,987	93,993	417,344	(299,947)
Operating income	24,562	14,369	87,871	620,197
Interest expense	(1)	(1)	(1,259)	(6,736)
Gain on derivative financial instruments	10,221	25,782	17,308	91,696
Other income (expense)	116	51	293	(10,161)
Equity income	0	0	0	0
Equity in earnings of subsidiaries	0	0	0	0
Total other income (expense)	10,336	25,832	16,342	74,799
Income before income taxes	34,898	40,201	104,213	694,996
Income tax expense (benefit)	0	0	0	0
Net income	34,898	40,201	104,213	694,996
Non-Guarantor Subsidiaries [Member]
Oil and natural gas	0	5,603	0	9,331
Oil and natural gas production	0	552	0	913
Gathering and transportation	0	307	0	599
Depreciation, depletion and amortization	149	2,076	953	3,322
Accretion of discount on asset retirement obligations	0	1	0	2
General and administrative	0	0	(1)	0
(Gain) loss on divestitures and other operating items	(276)	0	(1,282)	0
Total costs and expenses	(127)	2,936	(330)	4,836
Operating income	127	2,667	330	4,495
Interest expense	0	0	0	0
Gain on derivative financial instruments	0	0	0	0
Other income (expense)	0	0	0	0
Equity income	10,666	6,675	22,749	12,054
Equity in earnings of subsidiaries	0	0	0	0
Total other income (expense)	10,666	6,675	22,749	12,054
Income before income taxes	10,793	9,342	23,079	16,549
Income tax expense (benefit)	0	0	0	0
Net income	10,793	9,342	23,079	16,549
Eliminations [Member]
Oil and natural gas	0	0	0	0
Oil and natural gas production	0	0	0	0
Gathering and transportation	0	0	0	0
Depreciation, depletion and amortization	0	0	0	0
Accretion of discount on asset retirement obligations	0	0	0	0
General and administrative	0	0	0	0
(Gain) loss on divestitures and other operating items	0	0	0	0
Total costs and expenses	0	0	0	0
Operating income	0	0	0	0
Interest expense	0	0	0	0
Gain on derivative financial instruments	0	0	0	0
Other income (expense)	0	0	0	0
Equity income	0	0	0	0
Equity in earnings of subsidiaries	(45,691)	(49,543)	(127,292)	(711,545)
Total other income (expense)	(45,691)	(49,543)	(127,292)	(711,545)
Income before income taxes	(45,691)	(49,543)	(127,292)	(711,545)
Income tax expense (benefit)	0	0	0	0
Net income	$ (45,691)	$ (49,543)	$ (127,292)	$ (711,545)