Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based compensation
Total stock-based compensation	$ 2,427	$ 2,841	$ 4,934	$ 4,705
Unrecognized Compensation Cost	16,574		16,574
Stock options
Stock-based compensation
Unrecognized Compensation Cost	603		603
RSUs
Stock-based compensation
Unrecognized Compensation Cost	2,176		2,176
RSAs
Stock-based compensation
Unrecognized Compensation Cost	10,346		10,346
Research and development
Stock-based compensation
Total stock-based compensation	175	172	353	347
General and administrative
Stock-based compensation
Total stock-based compensation	2,252	$ 2,669	4,581	$ 4,358
Performance Contingent | RSAs
Stock-based compensation
Unrecognized Compensation Cost	107		107
Market-based | RSUs
Stock-based compensation
Unrecognized Compensation Cost	436		436
Market-based | RSAs
Stock-based compensation
Unrecognized Compensation Cost	$ 2,906		$ 2,906