CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating revenues:
Oil, gas, and NGL production revenue	$ 534,520	$ 312,608	$ 1,004,095	$ 675,203
Realized hedge gain (loss)	(1,189)	185	(1,288)	1,837
Gain (loss) on divestiture activity	6,280	(24,176)	5,706	(22,714)
Other operating revenues	19,749	15,803	35,027	27,517
Total operating revenues	559,360	304,420	1,043,540	681,843
Operating expenses:
Oil, gas, and NGL production expense	149,737	91,134	275,370	178,266
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	225,731	161,608	424,440	331,178
Exploration	20,657	22,007	36,055	40,614
Impairment of proved properties	34,552	38,523	55,771	38,523
Abandonment and impairment of unproved properties	4,339	10,707	4,641	10,849
General and administrative	35,374	31,130	67,654	59,272
Change in Net Profits Plan liability	(5,438)	(22,079)	(7,363)	(18,140)
Unrealized and realized derivative gain	(85,190)	(98,112)	(54,618)	(95,896)
Other operating expenses	35,314	17,111	51,108	28,561
Total operating expenses	415,076	252,029	853,058	573,227
Income from operations	144,284	52,391	190,482	108,616
Non-operating income (expense)
Interest income	24	5	36	75
Interest expense	(21,581)	(12,712)	(40,682)	(26,990)
Income before income taxes	122,727	39,684	149,836	81,701
Income tax expense	(46,205)	(14,795)	(56,587)	(30,476)
Net income	$ 76,522	$ 24,889	$ 93,249	$ 51,225
Basic weighted-average common shares outstanding	66,295	64,585	66,254	64,345
Diluted weighted-average common shares outstanding	67,893	67,556	67,711	67,806
Basic net income per common share	$ 1.15	$ 0.39	$ 1.41	$ 0.80
Diluted net income per common share	$ 1.13	$ 0.37	$ 1.38	$ 0.76
Dividends per common share	$ 0.00	$ 0.00	$ 0.05	$ 0.05