Consolidated Statement of Operations (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Revenues [Abstract]
Natural Gas Production Revenue	$ 249,835	$ 206,208	$ 481,751	$ 456,955
Oil and Condensate Revenue	30,732	22,180	56,107	44,557
Oil and Gas Revenue	280,567	228,388	537,858	501,512
Operating Expenses [Abstract]
Lease operating expenses	11,115	11,534	23,472	21,858
Production taxes	24,846	22,487	48,119	50,893
Gathering fees	13,910	12,498	26,917	24,453
Transportation charges	16,273	16,522	32,431	32,427
Depletion of Oil and Gas Properties	79,219	56,853	152,978	108,120
General and Administrative Expense	6,002	6,105	13,113	12,507
Costs and Expenses	151,365	125,999	297,030	250,258
Operating Income (Loss)	129,202	102,389	240,828	251,254
Other Nonoperating Income (Expense) [Abstract]
Interest Expense, Debt	(15,590)	(11,437)	(30,180)	(23,156)
Gain (loss) on commodity derivatives	47,606	14,566	63,241	195,917
Litigation Settlement, Expense	0	(9,902)	0	(9,902)
Other income (expense) net	(4)	22	16	173
Other Nonoperating Income (Expense)	32,012	(6,751)	33,077	163,032
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest	161,214	95,638	273,905	414,286
Income Tax Expense (Benefit)	57,709	34,145	101,679	150,417
Net Income (Loss)	$ 103,505	$ 61,493	$ 172,226	$ 263,869
Earnings Per Share, Basic [Abstract]
Earnings Per Share, Basic	$ 0.68	$ 0.40	$ 1.13	$ 1.73
Fully Diluted Earnings per Share:
Earnings Per Share, Diluted	$ 0.67	$ 0.40	$ 1.11	$ 1.71
Weighted Average Number of Shares Outstanding, Basic	152,899	152,300	152,749	152,187
Weighted Average Number of Shares Outstanding, Diluted	154,377	154,310	154,498	154,268