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	(1,532)	1			(1,533)
Stock-based compensation	7,978		7,978
Retirement of treasury stock	0		(1,533)		1,533
Issuance of common stock, merger	484,000	100	483,900
Net income (loss)	(101,203)			(101,203)
Balance at Sep. 30, 2018	987,797	210	1,769,852	(782,265)	0
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
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	(1,724)	1			(1,725)
Stock-based compensation	6,214		6,214
Retirement of treasury stock	0		(1,725)		1,725
Net income (loss)	(87,025)			(87,025)
Balance at Sep. 30, 2019	1,129,563	211	1,776,219	(646,867)	0
Balance at Jun. 30, 2019	1,116,393	210	1,774,164	(657,981)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock activity and shares exchanged for tax withholding	(218)	1			(219)
Stock-based compensation	2,274		2,274
Retirement of treasury stock	0		(219)		219
Net income (loss)	11,114			11,114
Balance at Sep. 30, 2019	$ 1,129,563	$ 211	$ 1,776,219	$ (646,867)	$ 0