CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Treasury Stock
Balance at Dec. 31, 2017	$ 598,554	$ 109	$ 1,279,507	$ (681,062)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock activity and shares exchanged for tax withholding	(1,462)				(1,462)
Stock-based compensation	4,185		4,185
Retirement of treasury stock	0		(1,462)		1,462
Issuance of common stock, merger	484,000	100	483,900
Net income (loss)	(24,937)			(24,937)
Balance at Mar. 31, 2018	1,060,340	209	1,766,130	(705,999)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock activity and shares exchanged for tax withholding	(28)				(28)
Stock-based compensation	1,797		1,797
Retirement of treasury stock	0		(28)		28
Net income (loss)	(46,906)			(46,906)
Balance at Jun. 30, 2018	1,015,203	209	1,767,899	(752,905)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock activity and shares exchanged for tax withholding	(42)	1			(43)
Stock-based compensation	1,996		1,996
Retirement of treasury stock	0		(43)		43
Net income (loss)	(29,360)			(29,360)
Balance at Sep. 30, 2018	987,797	210	1,769,852	(782,265)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock activity and shares exchanged for tax withholding	(2)				(2)
Stock-based compensation	1,880		1,880
Retirement of treasury stock	0		(2)		2
Net income (loss)	222,423			222,423
Balance at Dec. 31, 2018	1,212,098	210	1,771,730	(559,842)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock activity and shares exchanged for tax withholding	(1,484)				(1,484)
Stock-based compensation	2,090		2,090
Retirement of treasury stock	0		(1,484)		1,484
Net income (loss)	(96,229)			(96,229)
Balance at Mar. 31, 2019	$ 1,116,475	$ 210	$ 1,772,336	$ (656,071)	$ 0