Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	IPO [Member]	Public Offering [Member]	Common Stock [Member]	Common Stock [Member] IPO [Member]	Common Stock [Member] Public Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPO [Member]	Additional Paid-in Capital [Member] Public Offering [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balances at Dec. 31, 2014	$ 1,155,912			$ 1,600			$ 1,391,004				$ (236,144)	$ (548)
Beginning Balance, shares at Dec. 31, 2014				160,031,115
Stock-based compensation	4,635						4,635
Shares of common stock issued, value		$ 434,070			$ 625			$ 433,445
Shares of common stock issued, shares					62,500,000
Issuance of restricted stock				$ 1			(1)
Issuance of restricted stock, shares				132,496
Issuance of common stock upon vesting of equity- based compensation awards, net of shares withheld for income tax withholdings				$ 1			(1)
Issuance of common stock upon vesting of equity-based compensation awards, net of shares withheld for income tax withholdings, shares				10,659
Pension obligation adjustment	548											$ 548
Net income (loss)	(961,791)										(961,791)
Ending Balances at Dec. 31, 2015	633,374			$ 2,227			1,829,082				(1,197,935)
Ending Balance, shares at Dec. 31, 2015				222,674,270
Stock-based compensation	6,216						6,216
Shares of common stock issued, value			$ 123,813			$ 375			$ 123,438
Shares of common stock issued, shares						37,500,000
Issuance of restricted stock				$ 2			(2)
Issuance of restricted stock, shares				149,448
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				268,175
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				260,591,893
Stock-based compensation	9,301						9,301
Equity issuance costs	(44)						(44)
Issuance of restricted stock				$ 2			(2)
Issuance of restricted stock, shares				153,192
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				1,995,270
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				262,740,355