CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Treasury Stock
Balance (in shares) at Dec. 31, 2015		393,903
Balance at Dec. 31, 2015	$ 1,325,513	$ 3,939	$ 1,933,189	$ (564,686)	$ (46,929)
Increase (Decrease) in Shareholders' Equity
Equity-based compensation	41,447		43,391	(1,944)
Restricted stock awards and units (in shares)		1,956
Restricted stock awards and units	0	$ 20	(20)
Restricted stock forfeitures	0		2		(2)
Purchase of treasury stock	(1,981)		(1,315)		(666)
Net loss	(283,780)			(283,780)
Balance (in shares) at Dec. 31, 2016		395,859
Balance at Dec. 31, 2016	1,081,199	$ 3,959	1,975,247	(850,410)	(47,597)
Increase (Decrease) in Shareholders' Equity
Equity-based compensation	40,899		40,899
Restricted stock awards and units (in shares)		2,740
Restricted stock awards and units	0	$ 27	(27)
Purchase of treasury stock	(2,194)		(1,594)		(600)
Net loss	(222,792)			(222,792)
Balance (in shares) at Dec. 31, 2017		398,599
Balance at Dec. 31, 2017	897,112	$ 3,986	2,014,525	(1,073,202)	(48,197)
Increase (Decrease) in Shareholders' Equity
Acquisition of oil and gas properties (in shares)		34,994
Acquisition of oil and gas properties	307,944	$ 350	307,594
Equity-based compensation	36,464		36,464
Restricted stock awards and units (in shares)		9,322
Restricted stock awards and units	0	$ 93	(93)
Purchase of treasury stock	(206,051)		(17,241)		(188,810)
Net loss	(93,991)			(93,991)
Balance (in shares) at Dec. 31, 2018		442,915
Balance at Dec. 31, 2018	$ 941,478	$ 4,429	$ 2,341,249	$ (1,167,193)	$ (237,007)