Stock-Based Compensation - Employee 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 employee, director and non-employee stock-based compensation expense	$ 3,448	$ 2,033	$ 6,607	$ 3,993
General and administrative
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	1,416	874	2,884	1,826
Research and development
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 2,032	$ 1,159	$ 3,723	$ 2,167