CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues:
Oil, gas, and NGL production revenue	$ 1,499,905	$ 2,481,544	$ 2,199,550
Net gain on divestiture activity (note 3)	43,031	646	27,974
Marketed gas system revenue	9,485	24,897	60,039
Other operating revenues	4,544	15,220	5,811
Total operating revenues and other income	1,556,965	2,522,307	2,293,374
Operating Expenses
Oil, gas, and NGL production expense	723,633	715,878	597,045
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	921,009	767,532	822,872
Exploration	120,569	129,857	74,104
Impairment of proved properties	468,679	84,480	172,641
Abandonment and impairment of unproved properties	78,643	75,638	46,105
Impairment of other property and equipment	49,369	0	0
General and administrative	157,668	167,103	149,551
Change In Net Profits Plan Liability	(19,525)	(29,849)	(21,842)
Derivative gain	(408,831)	(583,264)	(3,080)
Marketed gas system expense	13,922	24,460	57,647
Other operating expenses	30,612	4,658	30,076
Total operating expenses	2,135,748	1,356,493	1,925,119
Income (loss) from operations	(578,783)	1,165,814	368,255
Non-operating income (expense):
Other, net	649	(2,561)	67
Interest expense	(128,149)	(98,554)	(89,711)
Loss on extinguishment of debt	(16,578)	0	0
Income (loss) before income taxes	(722,861)	1,064,699	278,611
Income tax (expense) benefit	275,151	(398,648)	(107,676)
Net income (loss)	$ (447,710)	$ 666,051	$ 170,935
Earnings Per Share, Basic [Abstract]
Basic weighted-average common shares outstanding	67,723	67,230	66,615
Basic net income (loss) per common share	$ (6.61)	$ 9.91	$ 2.57
Earnings Per Share, Diluted [Abstract]
Diluted weighted-average common shares outstanding	67,723	68,044	67,998
Diluted net income (loss) per common share	$ (6.61)	$ 9.79	$ 2.51