Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues
Oil, natural gas liquids and natural gas sales	$ 380,884	$ 249,114	$ 1,110,317	$ 644,212
Gain (loss) on derivative instruments, net	(154,628)	(57,610)	(188,242)	45,037
Total revenues	226,256	191,504	922,075	689,249
Operating Costs and Expenses
Oil, natural gas liquids and natural gas production	55,078	44,549	165,671	129,746
Production and ad valorem taxes	25,204	15,326	72,505	41,364
Depreciation, depletion and amortization	134,177	131,756	392,398	352,957
Asset impairment	178	100	428	1,589
Exploration	963	625	3,420	6,259
General and administrative (including stock-based compensation of $5,076 and $4,713 for the three months ended September 30, 2018 and 2017, respectively, and $13,839 and $11,101 for the nine months ended September 30, 2018 and 2017, respectively)	29,566	21,590	73,756	62,014
Accretion of discount on asset retirement obligations	1,604	1,473	4,704	4,330
Gain on sale of assets and other, net	(191)	(5,977)	(34,027)	(6,980)
Total operating costs and expenses	246,579	209,442	678,855	591,279
Operating Income (Loss)	(20,323)	(17,938)	243,220	97,970
Other Income (Expense)
Interest expense	(11,550)	(9,985)	(32,601)	(28,210)
Other income	1	231	693	1,006
Total other expense	(11,549)	(9,754)	(31,908)	(27,204)
Income (Loss) Before Income Taxes	(31,872)	(27,692)	211,312	70,766
Income tax expense (benefit)	(5,300)	(9,206)	50,695	26,368
Net Income (Loss)	$ (26,572)	$ (18,486)	$ 160,617	$ 44,398
Diluted Earnings Per Average Common Share (in dollars per share)	$ (0.27)	$ (0.19)	$ 1.64	$ 0.45
Basic Earnings Per Average Common Share (in dollars per share)	$ (0.27)	$ (0.19)	$ 1.65	$ 0.46
Diluted Average Common Shares Outstanding (in shares)	97,485	97,198	98,013	97,678
Basic Average Common Shares Outstanding (in shares)	97,485	97,198	97,413	97,176