Stock Options, Restricted Stock Units and Employee Stock Purchase Plan - Allocated Share-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,135	$ 3,525	$ 9,844	$ 6,446
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,956	2,890	6,270	4,939
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	275	0	537	0
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,904	$ 635	$ 3,037	$ 1,507