Summary of Significant Accounting Policies - Basic and Diluted Net (Loss) Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2014
Debt Instrument [Line Items]
Net (loss) income from continuing operations	$ (20,746)	$ (64,678)	$ (25,817)	$ (58,098)	$ 738	$ (155,713)	$ (14,252)	$ (35,925)	$ (169,339)	$ (205,153)	$ 2,093
Net income (loss) from discontinued operations	$ (1,531)	$ 95,517	$ 5,736	$ 3,856	$ 2,722	$ 3,652	$ 186	$ (635)	$ 103,578	$ 5,925	$ (4,576)
Weighted average common shares outstanding (in shares)									34,394	34,907	34,346
Effect of dilutive securities:
Stock options and RSUs (in shares)									0	0	487
Shares used in calculating dilutive net loss per share (in shares)									34,394	34,907	34,833
Basic net (loss) income per share:
(Loss) income from continuing operations (in dollars per share)	$ (0.60)	$ (1.88)	$ (0.75)	$ (1.70)	$ 0.02	$ (4.41)	$ (0.41)	$ (1.04)	$ (4.92)	$ (5.88)	$ 0.06
Income (loss) from discontinued operations (in dollars per share)	(0.04)	2.77	0.17	0.11	0.08	0.10	0.01	(0.02)	3.01	0.17	(0.13)
Total (in dollars per share)	(0.64)	0.89	(0.58)	(1.59)	0.10	(4.31)	(0.40)	(1.06)	(1.91)	(5.71)	(0.07)
Diluted net (loss) income per share:
(Loss) income from continuing operations (in dollars per share)	(0.60)	(1.88)	(0.75)	(1.70)	0.02	(4.41)	(0.41)	(1.04)	(4.92)	(5.88)	0.06
Income (loss) from discontinued operations (in dollars per share)	(0.04)	2.77	0.17	0.11	0.08	0.10	0.01	(0.02)	3.01	0.17	(0.13)
Total (in dollars per share)	$ (0.64)	$ 0.89	$ (0.58)	$ (1.59)	$ 0.10	$ (4.31)	$ (0.40)	$ (1.06)	$ (1.91)	$ (5.71)	$ (0.07)
Convertible Debt | Convertible Notes Due 2019
Debt Instrument [Line Items]
Interest rate												2.50%
Convertible Debt | 2022 Convertible Notes
Debt Instrument [Line Items]
Interest rate	3.25%						3.25%		3.25%