Long-Term Debt - Convertible Senior Notes Due 2023 (Details) $ / shares in Units, $ in Thousands			1 Months Ended		3 Months Ended
	Mar. 20, 2018 USD ($) $ / shares	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2012 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Nov. 01, 2016 USD ($)
Debt Instrument [Line Items]
Principal amount			$ 512,400		$ 512,400
Repayment of term loan					61,468	$ 6,409
Unamortized debt discount			33,177		33,177
Convertible Senior Notes Maturing September 2023
Debt Instrument [Line Items]
Principal amount	$ 125,000		125,000		125,000		$ 0
Net proceeds from debt issuance	$ 121,000
Interest rate (as a percent)	4.125%
Frequency of periodic payment	semi-annually
Maturity date	Sep. 15, 2023
Initial conversion ratio	0.1056133
Initial conversion price per share (in dollars per share) | $ / shares	$ 9.47
Redemption price as a percentage of principal amount	100.00%
Minimum percentage in aggregate principal amount	25.00%
Unamortized debt discount	$ 20,100		19,989		19,989
Carrying amount of equity component	$ 15,900
Effective interest rate (as a percent)	7.80%
Term Loan Maturing June 2020
Debt Instrument [Line Items]
Principal amount		$ 100,000	36,032		$ 36,032		97,500
Repayment of term loan			$ 61,000
Interest rate (as a percent)			6.13%		6.13%
Frequency of periodic payment		quarterly
Unamortized debt discount			$ 0		$ 0
Convertible Senior Notes Maturing March 2032
Debt Instrument [Line Items]
Principal amount			809	$ 200,000	809		60,115
Repurchased principal amount	$ 59,300							$ 125,000
Interest rate (as a percent)				3.25%
Maturity date				Mar. 15, 2032
Initial conversion ratio				0.0399752
Initial conversion price per share (in dollars per share) | $ / shares				$ 25.02
Redemption price as a percentage of principal amount				100.00%
Unamortized debt discount			$ 0	$ 35,400	$ 0		$ 500
Carrying amount of equity component				$ 22,500
Effective interest rate (as a percent)				6.90%