Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Stock Options [Member]	Restricted Stock [Member]	Common Stock [Member]	Treasury [Member]	Additional Paid In Capital [Member]	Additional Paid In Capital [Member] Stock Options [Member]	Additional Paid In Capital [Member] Restricted Stock [Member]	Retained Earnings [Member]
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Treasury Stock, Shares					(458,000)
Common stock, shares, outstanding at Dec. 31, 2015				64,956,000
Beginning Balance, value at Dec. 31, 2015	$ 342,643			$ 6,496	$ (3,759)	$ 475,823			$ (135,917)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net loss	(128,391)								(128,391)
Sale of common stock, net of offering costs, shares				12,075,000
Sale of common stock, net of offering costs, value	65,430			$ 1,208		64,222
Exercise of options and related income tax effect, shares				46,000
Exercise of options and related income tax effect, value	183			$ 5		178
Purchase of treasury stock, shares					(58,000)
Purchase of treasury stock, value	(124)				$ (124)
Income tax effect from share-based compensation, net		$ (1,264)	$ (1,023)				$ (1,264)	$ (1,023)
Issuance of restricted stock, shares				586,000
Issuance of restricted stock, value			0	$ 57				(57)
Stock-based compensation expense	3,944					3,944
Common stock, shares, outstanding at Dec. 31, 2016				77,663,000
Ending Balance, value at Dec. 31, 2016	281,398			$ 7,766	$ (3,883)	541,823			(264,308)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Treasury Stock, Shares					(516,000)
Net loss	(75,118)								(75,118)
Purchase of treasury stock, shares					(115,000)
Purchase of treasury stock, value	(533)				$ (533)
Issuance of restricted stock, shares				687,000
Issuance of restricted stock, value			0	$ 69				(69)
Stock-based compensation expense	$ 4,349					4,404
Cumulative Effect on Retained Earnings, Net of Tax | Adjustments for New Accounting Pronouncement [Member]									(55)
Common stock, shares, outstanding at Dec. 31, 2017	77,719,021			78,350,000
Ending Balance, value at Dec. 31, 2017	$ 210,096			$ 7,835	$ (4,416)	546,158			(339,481)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Treasury Stock, Shares					(631,000)
Net loss	(49,011)								(49,011)
Exercise of options and related income tax effect, shares				4,000
Exercise of options and related income tax effect, value	11					11
Purchase of treasury stock, shares					(159,000)
Purchase of treasury stock, value	(549)				$ (549)
Issuance of restricted stock, shares				651,000
Issuance of restricted stock, value			$ 0	$ 65				$ (65)
Stock-based compensation expense	4,444					4,444
Cumulative-effect adjustment due to adoption of ASC Topic 606	$ 67
Cumulative-effect adjustment due to adoption of ASC Topic 606 | Accounting Standards Update 2014-09 [Member]									67
Common stock, shares, outstanding at Dec. 31, 2018	78,214,550			79,005,000
Ending Balance, value at Dec. 31, 2018	$ 165,058			$ 7,900	$ (4,965)	$ 550,548			$ (388,425)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Treasury Stock, Shares					(790,000)