Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Components of convertible senior notes
Equity component net of equity issue costs	$ 60,222	$ 60,222
Principal amount	287,500	287,500
Unamortized discount	(12,090)	(22,076)
Unamortized debt issuance costs	(1,065)	(2,023)
Convertible senior notes, net carrying amount	$ 274,345	$ 263,401