Convertible Senior Notes - Schedule of Total Interest Expense Recognized Related to Notes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Convertible Senior Notes,
Contractual interest expense	$ 1,797	$ 1,797	$ 5,391	$ 5,390
Accretion of interest on milestone liability	500		1,449	0
Amortization of debt issuance costs	321	311	956	928
Total interest expense	$ 2,618	$ 2,108	$ 7,796	$ 6,318