Consolidated Statement of Operations (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenues [Abstract]
Natural Gas Production Revenue	$ 262,147	$ 217,890	$ 743,898	$ 674,845
Oil and Condensate Revenue	30,994	22,484	87,101	67,041
Oil and Gas Revenue	293,141	240,374	830,999	741,886
Operating Expenses [Abstract]
Lease operating expenses	12,381	10,850	35,853	32,708
Production taxes	25,676	23,191	73,796	74,084
Gathering fees	14,445	12,616	41,363	37,069
Transportation charges	16,061	16,201	48,492	48,628
Depletion of Oil and Gas Properties	85,795	59,674	238,773	167,795
General and Administrative Expense	6,185	5,957	19,298	18,464
Costs and Expenses	160,543	128,489	457,575	378,748
Operating Income (Loss)	132,598	111,885	373,424	363,138
Other Nonoperating Income (Expense) [Abstract]
Interest Expense, Debt	(15,902)	(11,382)	(46,082)	(34,538)
Gain (loss) on commodity derivatives	114,166	150,186	177,407	346,103
Litigation Settlement, Expense	0	0	0	(9,902)
Other income (expense) net	(3)	12	14	185
Other Nonoperating Income (Expense)	98,261	138,816	131,339	301,848
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest	230,859	250,701	504,763	664,986
Income Tax Expense (Benefit)	81,713	88,059	183,392	238,477
Net Income (Loss)	$ 149,146	$ 162,642	$ 321,371	$ 426,509
Earnings Per Share, Basic [Abstract]
Earnings Per Share, Basic	$ 0.98	$ 1.07	$ 2.10	$ 2.80
Fully Diluted Earnings per Share:
Earnings Per Share, Diluted	$ 0.97	$ 1.05	$ 2.08	$ 2.77
Weighted Average Number of Shares Outstanding, Basic	152,817	152,479	152,772	152,286
Weighted Average Number of Shares Outstanding, Diluted	154,280	154,192	154,418	154,241