Stock-Based Compensation - Employee expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 2,033	$ 1,193	$ 3,993	$ 2,300
General and administrative
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	874	520	1,826	1,035
Research and development
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 1,159	$ 673	$ 2,167	$ 1,265