Consolidated Statements of Stockholders' Investment (Equity) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Deficit)
Balance, shares at Dec. 31, 2014		37,925,164
Balance at Dec. 31, 2014	$ 524,287	$ 379	$ 390,725	$ 133,183
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs, shares		265,734
Issuance of common stock, net of issuance costs	4,011	$ 3	4,008
Issuance of restricted stock units, net of taxes paid, shares		74,971
Issuance of restricted stock units, net of taxes paid	(929)	$ 1	(930)
Issuance costs from secondary stock offering	(225)		(225)
Share-based compensation	2,500		2,500
Tax benefit (deficiency) on share-based compensation	1,175		1,175
Net income (loss)	25,620			25,620
Balance at Dec. 31, 2015	556,439	$ 383	397,253	158,803
Balance, shares at Dec. 31, 2015		38,265,869
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock units, net of taxes paid, shares		74,738
Issuance of restricted stock units, net of taxes paid	(303)	$ 0	(303)
Issuance costs from secondary stock offering	(33)		(33)
Share-based compensation	2,232		2,232
Tax benefit (deficiency) on share-based compensation	(547)		(547)
Net income (loss)	(360,320)			(360,320)
Balance at Dec. 31, 2016	$ 197,468	$ 383	398,602	(201,517)
Balance, shares at Dec. 31, 2016	38,341,000	38,340,607
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock units, net of taxes paid, shares		82,499
Issuance of restricted stock units, net of taxes paid	$ (239)	$ 1	(240)
Share-based compensation	2,233		2,233
Proceeds from Issuance of Warrants	2,571		2,571
Net income (loss)	(91,186)			(91,186)
Balance at Dec. 31, 2017	$ 110,847	$ 384	$ 403,166	$ (292,703)
Balance, shares at Dec. 31, 2017	38,423,000	38,423,106