Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation
Total stock-based compensation expense	$ 2,472	$ 1,718	$ 7,406	$ 6,423
Total unrecognized compensation cost	13,788		13,788
Stock options
Stock-based compensation
Total unrecognized compensation cost	455		455
RSUs
Stock-based compensation
Total unrecognized compensation cost	1,623		1,623
RSAs
Stock-based compensation
Total unrecognized compensation cost	8,887		8,887
Research and development
Stock-based compensation
Total stock-based compensation expense	180	143	533	490
General and administrative
Stock-based compensation
Total stock-based compensation expense	2,292	$ 1,575	6,873	$ 5,933
Performance Contingent | RSAs
Stock-based compensation
Total unrecognized compensation cost	38		38
Market-based | RSUs
Stock-based compensation
Total unrecognized compensation cost	360		360
Market-based | RSAs
Stock-based compensation
Total unrecognized compensation cost	$ 2,425		$ 2,425