Stock-Based Compensation - Equity Incentive Plan Terms (Details) - shares
1 Months Ended 12 Months Ended
Jan. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Stock Options Subject to Right of Repurchase      
Award terms      
Number of shares early exercised, subject to repurchase   0 5,000
Equity Incentive Plans      
Stock-Based compensation      
Shares available for future grants   1,521,843  
Equity Incentive Plans | Stock options      
Award terms      
Term of grant (in years)   10 years  
Equity Incentive Plans | One Year Cliff | Stock options      
Award terms      
Vesting period   1 year  
Equity Incentive Plans | Second Offering Period | Stock options      
Award terms      
Vesting period   36 months  
2015 Equity Incentive Plan      
Stock-Based compensation      
Initial shares available for grant from equity incentive plan 2,500,000    
Plan terms      
Number of shares option, minimum annual increase in number of shares reserved for issuance 1,750,000    
Percentage of common stock outstanding option, minimum annual increase in number of shares reserved for issuance (as a percent) 5.00%    
Plan term (in years) 10 years    
2010 Equity Incentive Plan      
Stock-Based compensation      
Maximum shares available for grant transferred between equity incentive plans. 4,537,868