Long-Term Debt - Convertible Senior Notes Due 2023 (Details) $ / shares in Units, $ in Thousands			1 Months Ended		6 Months Ended
	Mar. 20, 2018 USD ($) $ / shares	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2012 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	May 04, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Principal amount					$ 502,195
Repayment of term loan					61,936	$ 192,258
Unamortized debt discount					31,878
Convertible Senior Notes Maturing September 2023
Debt Instrument [Line Items]
Principal amount	$ 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				19,394
Carrying amount of equity component	$ 15,900
Effective interest rate (as a percent)	7.80%
Convertible Senior Notes Maturing March 2032 (Redeemed May 2018)
Debt Instrument [Line Items]
Principal amount				$ 200,000	0			60,115
Repurchased principal amount	$ 59,300						$ 800
Interest rate (as a percent)				3.25%
Maturity date				Mar. 15, 2032
Term Loan Maturing June 2020
Debt Instrument [Line Items]
Principal amount		$ 100,000			$ 35,564	$ 100,000		$ 97,500
Repayment of term loan			$ 61,000
Interest rate (as a percent)					6.34%
Frequency of periodic payment		quarterly
Unamortized debt discount					$ 0