CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Operating revenues and other income:
Oil, gas, and NGL production revenue	$ 2,199,550		$ 1,473,868		$ 1,332,392
Realized hedge (loss) gain	(1,777)		3,866		(20,707)
Gain (loss) on divestiture activity	27,974		(27,018)		220,676
Marketed gas system revenue	60,039		52,808		69,898
Other operating revenue	7,588		1,578		1,059
Total operating revenues and other income	2,293,374		1,505,102		1,603,318
Operating Expenses
Oil, gas, and NGL production expense	597,045		391,872		290,111
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	822,872		727,877		511,103
Exploration	74,104		90,248		53,537
Impairment of proved properties	172,641		208,923		219,037
Abandonment and impairment of unproved properties	46,105		16,342		7,367
General and administrative	149,551		119,815		118,526
Change in Net Profits Plan liability	(21,842)		(28,904)		(25,477)
Derivative gain	(3,080)	[1]	(55,630)	[1]	(37,086)	[1]
Marketed gas system expense	57,647		47,583		64,249
Other operating expense	30,076		6,993		17,567
Total operating expenses	1,925,119		1,525,119		1,218,934
Income (loss) from operations	368,255		(20,017)		384,384
Nonoperating income (expense):
Interest income	67		220		466
Interest expense	(89,711)		(63,720)		(45,849)
Income (loss) before income taxes	278,611		(83,517)		339,001
Income tax (expense) benefit	(107,676)		29,268		(123,585)
Net income (loss)	$ 170,935		$ (54,249)		$ 215,416
Basic weighted-average common shares outstanding	66,615		65,138		63,755
Diluted weighted-average common shares outstanding	67,998		65,138		67,564
Basic net income (loss) per common share	$ 2.57		$ (0.83)		$ 3.38
Diluted net income (loss) per common share	$ 2.51		$ (0.83)		$ 3.19

[1] Total derivative gain is reported in the derivative gain line item on the consolidated statements of cash flows within net cash provided by operating activities.