Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Components of convertible senior notes
Equity component net of equity issue costs	$ 60,222	$ 60,222
Principal amount	287,500	287,500
Unamortized discount	(40,752)	(46,614)
Convertible senior notes, net carrying amount	$ 246,748	$ 240,886