Stock-Based Compensation - Employee expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 8,231	$ 9,303	$ 14,743	$ 15,159
Employee stock options
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	6,667	8,946	12,549	14,470
ESPP
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	213	195	407	413
Restricted stock units
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	1,351	162	1,787	276
General and administrative
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	2,804	2,008	5,095	3,862
Research and development
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 5,427	$ 7,295	$ 9,648	$ 11,297