Convertible Preferred Stock and Stockholders' Equity (Details 4) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Convertible preferred stock
Total stock-based compensation expense	$ 973	$ 786	$ 1,840	$ 1,583
Research And Development
Convertible preferred stock
Total stock-based compensation expense	580	450	1,149	892
General And Administrative
Convertible preferred stock
Total stock-based compensation expense	$ 393	$ 336	$ 691	$ 691