CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Oil, natural gas liquids and natural gas sales	$ 987,438	$ 621,366	$ 763,261
Gain (loss) on derivative instruments, net	(26,393)	(88,477)	115,293
Total revenues	961,045	532,889	878,554
Operating Costs and Expenses
Oil, natural gas liquids and natural gas production	183,697	171,714	228,380
Production and ad valorem taxes	59,447	42,938	57,380
Depreciation, depletion and amortization	483,376	447,961	593,789
Asset impairment	1,671	220,652	1,292,308
Exploration	10,075	5,415	14,878
General and administrative (including stock-based compensation of $15,402, $19,641 and $12,910 for the years ended December 31, 2017, 2016 and 2015, respectively)	84,823	95,689	149,132
Accretion of discount on asset retirement obligations	5,831	6,672	7,108
Gain on sale of assets and other, net	(13,011)	(246,922)	(26,570)
Total operating costs and expenses	815,909	744,119	2,316,405
Operating Income (Loss)	145,136	(211,230)	(1,437,851)
Other Income (Expense)
Interest expense	(38,366)	(36,899)	(43,108)
Other income	617	978	223
Total other expense	(37,749)	(35,921)	(42,885)
Income (Loss) Before Income Taxes	107,387	(247,151)	(1,480,736)
Income tax benefit	(199,441)	(79,638)	(535,005)
Net Income (Loss)	$ 306,828	$ (167,513)	$ (945,731)
Diluted Earnings Per Average Common Share (in dollars per share)	$ 3.14	$ (1.77)	$ (12.43)
Basic Earnings Per Average Common Share (in dollars per share)	$ 3.16	$ (1.77)	$ (12.43)
Diluted Average Common Shares Outstanding (in shares)	97,707,408	94,475,797	76,078,371
Basic Average Common Shares Outstanding (in shares)	97,182,477	94,475,797	76,078,371