Debt (Details 1) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest expense on convertible senior notes
Convertible senior notes, contractual interest expense	$ 718	$ 718	$ 2,156	$ 2,156
Amortization of debt issuance costs	319	320	958	959
Amortization of debt discount	3,379	3,181	9,986	9,405
Convertible senior notes, total interest expense	$ 4,416	$ 4,219	$ 13,100	$ 12,520
Convertible senior notes, effective interest rate during period	6.50%	6.50%	6.50%	6.50%