CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenues and other income:
Oil, gas, and NGL production revenue	$ 1,253,783	$ 1,178,426	$ 1,499,905
Net gain (loss) on divestiture activity	(131,028)	37,074	43,031
Other operating revenues	6,621	1,950	14,029
Total operating revenues and other income	1,129,376	1,217,450	1,556,965
Operating Expenses:
Oil, gas, and NGL production expense	507,906	597,565	723,633
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	557,036	790,745	921,009
Exploration	56,179	65,641	120,569
Impairment of proved properties	3,806	354,614	468,679
Abandonment and impairment of unproved properties	12,272	80,367	78,643
Impairment of other property and equipment	0	0	49,369
General and administrative	120,585	126,428	157,668
Net derivative (gain) loss	26,414	250,633	(408,831)
Other operating expenses	13,667	10,772	25,009
Total operating expenses	1,297,865	2,276,765	2,135,748
Loss from operations	(168,489)	(1,059,315)	(578,783)
Non-operating income (expense):
Interest expense	(179,257)	(158,685)	(128,149)
Gain (loss) on extinguishment of debt	(35)	15,722	(16,578)
Other, net	3,968	362	649
Loss before income taxes	(343,813)	(1,201,916)	(722,861)
Income tax benefit	182,970	444,172	275,151
Net loss	$ (160,843)	$ (757,744)	$ (447,710)
Earnings Per Share, Basic [Abstract]
Basic weighted-average common shares outstanding	111,428	76,568	67,723
Basic net loss per common share	$ (1.44)	$ (9.90)	$ (6.61)
Earnings Per Share, Diluted [Abstract]
Diluted weighted-average common shares outstanding	111,428	76,568	67,723
Diluted net loss per common share	$ (1.44)	$ (9.90)	$ (6.61)