Convertible Preferred Stock and Stockholders' Equity (Details 4) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Convertible preferred stock
Total stock-based compensation expense	$ 871	$ 783	$ 2,711	$ 2,365
Research And Development
Convertible preferred stock
Total stock-based compensation expense	450	461	1,599	1,352
General And Administrative
Convertible preferred stock
Total stock-based compensation expense	$ 421	$ 322	$ 1,112	$ 1,013