Net (Loss) Income Per Share - Computation of Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Basic weighted average shares outstanding (shares)	110,345,135		102,597,059		109,744,405	101,747,416
Diluted average shares outstanding (in shares)	110,345,135		112,617,151		109,744,405	101,747,416
Net (loss) income as reported	$ (28,395)	$ (19,155)	$ 13,744	$ (15,816)	$ (47,550)	$ (2,074)
Interest attributable to 2013 Convertible Notes	0		886		0	0
Net (loss) income for diluted earnings per share	$ (28,395)		$ 14,630		$ (47,550)	$ (2,074)
Net (loss) income per share - basic ($ per share)	$ (0.26)		$ 0.13		$ (0.43)	$ (0.02)
Net (loss) income per share - diluted ($ per share)	$ (0.26)		$ 0.13		$ (0.43)	$ (0.02)
2013 Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted average shares outstanding (in shares)	0		3,854,959		0	0
Common stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted average shares outstanding (in shares)	0		3,870,462		0	0
Restricted stock awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted average shares outstanding (in shares)	0		1,797,089		0	0
Restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted average shares outstanding (in shares)	0		245,214		0	0
Common stock warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted average shares outstanding (in shares)	0		252,368		0	0