Stock-Based Compensation - Employee Stock Purchase Plan (Details)
1 Months Ended 6 Months Ended
Mar. 05, 2015
$ / shares
Jan. 31, 2015
USD ($)
offering_period
shares
Jun. 30, 2015
USD ($)
shares
Dec. 31, 2014
shares
Stock-Based compensation        
Total shares reserved     6,570,241 18,423,941
2015 Employee Stock Purchase Plan        
Stock-Based compensation        
Maximum percentage of eligible compensation per employee to purchase shares of common stock   15.00%    
Maximum number of shares per offering period per employee   1,500    
Maximum share value per calendar year per employee | $   $ 25,000    
Employee purchase price, percentage of fair market value of common stock 85.00% 85.00%    
Fair market value of common stock at beginning of offering period (in usd per share) | $ / shares $ 11.50      
Accumulated employee withholdings | $     $ 600,000  
Number of employment hours requirement per week during requisite service period   20 hours    
Offering period, maximum   27 months    
Number of offering periods under terms of plan | offering_period   2    
Offering periods beginning on May 1 and November 1   6 months    
Total shares reserved   375,000 375,000  
Number of shares option, minimum annual increase in number of shares reserved for issuance   250,000    
Percentage of common stock outstanding option, minimum annual increase in number of shares reserved for issuance (as a percent)   1.00%    
Unrecognized compensation cost related to nonvested share-based compensation arrangements | $     $ 300,000  
Expected weighted-average period for recognition of unrecognized stock-based compensation costs (in years)     3 months 18 days  
2015 Employee Stock Purchase Plan | Minimum        
Stock-Based compensation        
Requisite service period for award eligibility per year   5 months