Stock-Based Compensation - Employee Stock Purchase Plan (Details)
1 Months Ended 12 Months Ended
Oct. 30, 2015
$ / shares
Mar. 05, 2015
$ / shares
Jan. 31, 2015
USD ($)
offering_period
shares
Dec. 31, 2015
USD ($)
offering_period
shares
Nov. 01, 2015
$ / shares
Dec. 31, 2014
shares
Stock-Based compensation            
Total shares reserved       6,261,008   18,423,941
Intrinsic value of shares of stock purchased under ESPP | $       $ 100,000    
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% 85.00%      
Number of offering periods under terms of plan | offering_period     2 2    
Fair market value of common stock (in usd per share) | $ / shares $ 4.82 $ 11.50     $ 4.89  
Offering periods beginning on May 1 and November 1     6 months      
Issuance of common stock under employee stock purchase plan (in shares)       133,728    
Accumulated employee withholdings | $       $ 200,000    
Number of employment hours requirement per week during requisite service period     20 hours      
Offering period, maximum     27 months      
Total shares reserved     375,000 241,272   0
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%      
Discount on purchase of stock (as a percent)       15.00%    
Unrecognized compensation cost related to nonvested share-based compensation arrangements | $       $ 100,000    
Expected weighted-average period for recognition of unrecognized stock-based compensation costs (in years)       3 months 29 days    
2015 Employee Stock Purchase Plan | Call Option            
Stock-Based compensation            
Fair value of option (as a percent)       85.00%    
2015 Employee Stock Purchase Plan | Put Option            
Stock-Based compensation            
Fair value of option (as a percent)       15.00%    
2015 Employee Stock Purchase Plan | Minimum            
Stock-Based compensation            
Requisite service period for award eligibility per year     5 months