CONDENSED CONSOLIDATED STATEMENTS 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
Operating revenues and other income:
Oil, gas, and NGL production revenue	$ 333,934	$ 175,887	$ 610,247	$ 388,774
Realized hedge gain (loss) (note 10)	(6,330)	9,329	(7,705)	11,924
Gain on divestiture activity (note 3)	30,019	7,021	54,934	127,999
Marketed gas system and other operating revenue	20,250	19,460	35,726	43,135
Total operating revenues and other income	377,873	211,697	693,202	571,832
Operating expenses:
Oil, gas, and NGL production expense	53,342	45,168	119,154	93,508
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	115,382	79,770	220,738	157,535
Exploration	9,603	14,498	22,315	28,396
Abandonment and impairment of unproved properties	1,237	2,375	4,316	3,279
General and administrative	27,310	25,398	53,171	48,884
Change in Net Profits Plan liability	(13,984)	(6,599)	211	(33,871)
Unrealized and realized derivative (gain) loss (note 10)	(43,876)	(2,087)	44,553	(9,822)
Marketed gas system and other expense	17,152	16,385	37,009	39,383
Total operating expenses	166,166	174,908	501,467	327,292
Income from operations	211,707	36,789	191,735	244,540
Nonoperating income (expense):
Interest income	227	54	355	183
Interest expense	(14,550)	(6,343)	(24,264)	(13,130)
Income before income taxes	197,384	30,500	167,826	231,593
Income tax expense	(72,851)	(12,432)	(61,796)	(87,347)
Net income	$ 124,533	$ 18,068	$ 106,030	$ 144,246
Basic weighted-average common shares outstanding (in shares)	63,638	62,917	63,543	62,855
Diluted weighted-average common shares outstanding (in shares)	66,909	64,566	66,695	64,493
Basic net income per common share (in dollars per share)	$ 1.96	$ 0.29	$ 1.67	$ 2.29
Diluted net income per common share (in dollars per share)	$ 1.86	$ 0.28	$ 1.59	$ 2.24