Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues and other income
Oil, natural gas, and related product sales	$ 1,089,666	$ 935,751	$ 1,213,026
CO2 sales and transportation fees	26,182	24,816	30,626
Interest income and other income	13,938	15,029	13,908
Total revenues and other income	1,129,786	975,596	1,257,560
Expenses
Lease operating expenses	447,799	414,937	515,043
Marketing and plant operating expenses	51,820	57,454	55,746
CO2 discovery and operating expenses	3,099	3,374	4,557
Taxes other than income	87,207	77,892	109,992
General and administrative expenses	101,806	109,926	144,564
Interest, net of amounts capitalized of $30,762, $25,982 and $32,146, respectively	99,263	125,145	159,268
Depletion, depreciation, and amortization	207,713	846,043	531,660
Commodity derivatives expense (income)	77,576	127,944	(147,999)
Gain on debt extinguishment	0	(115,095)	0
Write-down of oil and natural gas properties	0	810,921	4,939,600
Impairment of goodwill	0	0	1,261,512
Other expenses	7,003	37,402	9,599
Total expenses	1,083,286	2,495,943	7,583,542
Income (loss) before income taxes	46,500	(1,520,347)	(6,325,982)
Income tax benefit	(116,652)	(544,170)	(1,940,534)
Net income (loss)	$ 163,152	$ (976,177)	$ (4,385,448)
Net income (loss) per common share
Basic	$ 0.42	$ (2.61)	$ (12.57)
Diluted	0.41	(2.61)	(12.57)
Dividends declared per common share	$ 0	$ 0	$ 0.1875
Weighted average common shares outstanding
Basic	390,928	373,859	348,802
Diluted	395,921	373,859	348,802