CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Operating revenues and other income:
Oil, gas, and NGL production revenue	$ 312,608	$ 333,934	$ 675,203	$ 610,247
Realized hedge gain (loss) (note 10)	185	(6,330)	1,837	(7,705)
Gain on divestiture activity (note 3)	(24,176)	30,019	(22,714)	54,934
Marketed gas system and other operating revenue	15,803	20,250	27,517	35,726
Total operating revenues and other income	304,420	377,873	681,843	693,202
Operating expenses:
Oil, gas, and NGL production expense	91,134	53,342	178,266	119,154
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	161,608	115,382	331,178	220,738
Exploration	22,007	9,603	40,614	22,315
Impairment of proved properties	38,523	0	38,523	0
Abandonment and impairment of unproved properties	10,707	1,237	10,849	4,316
General and administrative	31,130	27,310	59,272	53,171
Change in Net Profits Plan liability (note 7)	(22,079)	(13,984)	(18,140)	211
Unrealized and realized derivative (gain) loss (note 10)	(98,112)	(43,876)	(95,896)	44,553
Marketed gas system and other expense	17,111	17,152	28,561	37,009
Total operating expenses	252,029	166,166	573,227	501,467
Income from operations	52,391	211,707	108,616	191,735
Nonoperating income (expense):
Interest income	5	227	75	355
Interest expense	(12,712)	(14,550)	(26,990)	(24,264)
Income before income taxes	39,684	197,384	81,701	167,826
Income tax expense	(14,795)	(72,851)	(30,476)	(61,796)
Net income	$ 24,889	$ 124,533	$ 51,225	$ 106,030
Basic weighted-average common shares outstanding (in shares)	64,585	63,638	64,345	63,543
Diluted weighted-average common shares outstanding (in shares)	67,556	66,909	67,806	66,695
Basic net income per common share (in dollars per share) (note 9)	$ 0.39	$ 1.96	$ 0.80	$ 1.67
Diluted net income per common share (in dollars per share) (note 9)	$ 0.37	$ 1.86	$ 0.76	$ 1.59
Cash dividends (in dollars per share)	$ 0.00	$ 0.00	$ 0.05	$ 0.05

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets. Amount of accretion expense recognized in the income statement during the period that is associated with asset retirement obligations. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. Such accretion expense representing changes in the liability for an asset retirement obligation due to passage of time is the result of applying an interest method of allocation to the amount of the liability at the beginning of the period. The interest rate used to measure that change shall be the credit-adjusted risk-free rate that existed when the liability, or portion thereof, was initially measured. That amount shall be recognized as an increase in the carrying amount of the liability and as an expense classified as an operating item in the statement of income. Accretion expense shall not be considered to be interest cost for purposes of capitalization of interest.

No definition available.