Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Stock-based compensation
Total stock-based compensation	$ 2,507	$ 1,864
Unrecognized Compensation Cost	17,864
Stock options
Stock-based compensation
Unrecognized Compensation Cost	750
RSUs
Stock-based compensation
Unrecognized Compensation Cost	1,488
RSAs
Stock-based compensation
Unrecognized Compensation Cost	11,558
Research and development
Stock-based compensation
Total stock-based compensation	178	175
General and administrative
Stock-based compensation
Total stock-based compensation	2,329	$ 1,689
Performance Contingent | RSAs
Stock-based compensation
Unrecognized Compensation Cost	175
Market Contingent | RSUs
Stock-based compensation
Unrecognized Compensation Cost	510
Market Contingent | RSAs
Stock-based compensation
Unrecognized Compensation Cost	$ 3,383