Equity Award Plans - Unrecognized Compensation Cost (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Series A convertible preferred stock  
Unrecognized compensation cost  
Unrecognized compensation cost $ 1,110
Weighted-average period for unrecognized compensation cost 2 years 4 months 2 days
Common Stock  
Unrecognized compensation cost  
Unrecognized compensation cost $ 24,239
Weighted-average period for unrecognized compensation cost 2 years 8 months 12 days