Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Public Offering [Member]	Common Stock [Member]	Common Stock [Member] Public Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Public Offering [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]
Beginning Balances at Dec. 31, 2015	$ 633,374		$ 2,227		$ 1,829,082			$ (1,197,935)
Beginning Balance, shares at Dec. 31, 2015			14,844,951
Stock-based compensation	6,216				6,216
Shares of common stock issued, value		$ 123,813		$ 375		$ 123,438
Shares of common stock issued, shares				2,500,000
Issuance of restricted stock			$ 2		(2)
Issuance of restricted stock, shares			9,963
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings	(61)		$ 3		(3)		$ (61)
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings, shares			17,878
Net income (loss)	(206,735)							(206,735)
Ending Balances at Dec. 31, 2016	556,607		$ 2,607		1,958,731		(61)	(1,404,670)
Ending Balance, shares at Dec. 31, 2016			17,372,793
Stock-based compensation	9,301				9,301
Equity issuance costs	(44)				(44)
Issuance of restricted stock			$ 2		(2)
Issuance of restricted stock, shares			10,213
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings	(2,035)		$ 28		(28)		(2,035)
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings, shares			133,018
Net income (loss)	8,525							8,525
Ending Balances at Dec. 31, 2017	572,354		$ 2,637		1,967,958		(2,096)	(1,396,145)
Ending Balance, shares at Dec. 31, 2017			17,516,024
Stock-based compensation	7,891				7,891
Equity issuance costs	(344)				(344)
Shares of common stock issued in asset acquisition, net of equity issuance costs	90,020		$ 378		89,642
Shares of common stock issued in asset acquisition, net of equity issuance costs, shares			2,521,573
Issuance of restricted stock			$ 2		(2)
Issuance of restricted stock, shares			15,476
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings	(1,261)		$ 26		(26)		(1,261)
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings, shares			115,990
Net income (loss)	18,826							18,826
Ending Balances at Dec. 31, 2018	$ 687,486		$ 3,043		$ 2,065,119		$ (3,357)	$ (1,377,319)
Ending Balance, shares at Dec. 31, 2018			20,169,063