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Equity Incentive Plans - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation expense $ 3,332 $ 2,448 $ 6,378 $ 5,550
Unrecognized share-based compensation expense related to unvested stock options $ 33,200   $ 33,200  
Unrecognized share-based compensation expense related to unvested stock options, weighted-average period for recognition     3 years 1 month 28 days  
Option Valuation Model        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected dividend yield     0.00%  
2009 Equity Incentive Plan | Options        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Number of shares available for issuance 20,837,404   20,837,404  
2009 Equity Incentive Plan | Options | Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Option expiration period     10 years