Stock-Based Compensation - Employee expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 3,158	$ 1,960
General and administrative
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	1,467	952
Research and development
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 1,691	$ 1,008