CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Operating revenues and other income:
Oil, gas, and NGL production revenue	$ 373,928	$ 325,231	$ 1,049,131	$ 935,478
Gain (Loss) on Derivative Instruments, Net, Pretax	501	(6,843)	2,338	(14,548)
Gain on divestiture activity (note 3)	(8,532)	190,728	(31,246)	245,662
Marketed gas system and other operating revenue	13,054	21,458	40,571	57,184
Total operating revenues and other income	378,951	530,574	1,060,794	1,223,776
Operating expenses:
Oil and Gas Production Expense	102,447	77,753	280,713	196,907
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	192,432	123,067	523,610	343,805
Exploration	25,417	11,272	66,031	33,587
Impairment of proved properties	0	48,525	38,523	48,525
Abandonment and impairment of unproved properties	447	0	11,296	4,316
General and administrative	32,171	29,787	91,443	82,958
Change in Net Profits Plan liability (note 7)	798	(24,930)	(17,342)	(24,719)
Unrealized and Realized Derivative (Gain) Loss	55,856	(128,425)	(40,040)	(83,872)
Gas Gathering, Transportation, Marketing and Processing Costs	12,219	20,737	40,780	57,746
Total operating expenses	421,787	157,786	995,014	659,253
Income from operations	(42,836)	372,788	65,780	564,523
Nonoperating income (expense):
Interest income	126	27	201	382
Interest expense	(18,362)	(9,372)	(45,352)	(33,636)
Income before income taxes	(61,072)	363,443	20,629	531,269
Income tax benefit (expense)	22,736	(133,346)	(7,740)	(195,142)
Net income	$ (38,336)	$ 230,097	$ 12,889	$ 336,127
Basic weighted-average common shares outstanding (in shares)	65,745	63,904	64,815	63,665
Diluted weighted-average common shares outstanding (in shares)	65,745	67,386	67,343	67,390
Basic net income per common share (in dollars per share) (note 9)	$ (0.58)	$ 3.60	$ 0.20	$ 5.28
Diluted net income per common share (in dollars per share) (note 9)	$ (0.58)	$ 3.41	$ 0.19	$ 4.99
Cash dividends (in dollars per share)	$ 0.05	$ 0.05	$ 0.10	$ 0.10

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.