Income (Loss) per Share - Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share Reconciliation [Abstract]
Net income	$ (83,891)	$ 28,169	$ 61,092	$ (5,822)	$ 16,178	$ 15,185	$ 5,370	$ 25,541
Undistributed income allocated to participating securities	0			0			59	361
Net income (loss) attributable to common stockholders	(83,891)			(5,822)			5,311	25,180
Plus: Net income effect of convertible securities	0			0			0	0
Numerator for diluted income (loss) per common share	$ (83,891)			$ (5,822)			$ 5,311	$ 25,180
Basic weighted-average common stock shares outstanding (in shares)	50,942			45,709			49,973	45,676
Dilutive effects of common stock equivalents (in shares)	0			0			98	45
Diluted weighted-average common stock shares outstanding (in shares)	50,942			45,709			50,071	45,721
Basic income (loss) per share (in dollars per share)	$ (1.65)			$ (0.13)			$ 0.11	$ 0.55
Diluted income (loss) per share (in dollars per share)	$ (1.65)			$ (0.13)			$ 0.11	$ 0.55
5.00% Convertible Senior Notes due 2021
Earnings Per Share Reconciliation [Abstract]
Debt instrument, interest rate	5.00%						5.00%
Restricted Stock Awards
Earnings Per Share Reconciliation [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)							160	33
Stock Option Awards
Earnings Per Share Reconciliation [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)							1,800	1,300
Convertible Debt Securities
Earnings Per Share Reconciliation [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	4,400			6,400			5,500	6,400
Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average number of shares issuable under the common stock warrants (in shares)	354			354			354	354