Summary of Significant Accounting Policies - Basic and Diluted Net (Loss) Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Aug. 31, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2014
Debt Instrument [Line Items]
Net (loss) income										$ (199,228)	$ (2,483)	$ 32,779
Weighted average common shares outstanding										34,907	34,346	31,471
Effect of dilutive securities:
Warrants (in shares)										0	0	2,466
Stock options and RSUs (in shares)										0	0	1,371
Shares used in calculating dilutive net (loss) income per share (in shares)										34,907	34,346	35,308
Net (loss) income per share:
Basic (USD per share)		$ 0.10	$ (4.31)	$ (0.40)	$ (1.06)	$ (0.31)	$ 0.47	$ (0.02)	$ (0.22)	$ (5.71)	$ (0.07)	$ 1.04
Diluted (USD per share)		$ 0.10	$ (4.31)	$ (0.40)	$ (1.06)	$ (0.31)	$ 0.43	$ (0.02)	$ (0.22)	$ (5.71)	$ (0.07)	$ 0.93
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%
Debt term										5 years
Line of Credit | 2015 Term Loan Facility
Debt Instrument [Line Items]
Debt term	6 years
Maximum borrowing capacity	$ 350,000