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Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Stock options      
Outstanding at beginning of period (in shares) 1,226,140    
Granted (in shares) 606,942    
Exercised (in shares) (40,548)    
Cancelled or forfeited (in shares) (68,980)    
Outstanding at end of period (in shares) 1,723,554 1,226,140  
Exercisable at end of period (in shares) 795,501    
Vested or expected to vest at end of period (in shares) 1,607,456    
Weighted-Average Exercise Price      
Outstanding at beginning of period (in dollars per share) $ 4.14    
Granted (in dollars per share) 11.42    
Exercised (in dollars per share) 2.24    
Cancelled or forfeited (in dollars per share) 6.49    
Outstanding at end of period (in dollars per share) 6.66 $ 4.14  
Exercisable at end of period (in dollars per share) 3.47    
Vested or expected to vest at end of period (in dollars per share) $ 6.40    
Weighted-Average Remaining Contractual Term      
Outstanding at beginning of period 7 years 11 months 1 day 8 years 1 month 24 days  
Outstanding at end of period 7 years 11 months 1 day 8 years 1 month 24 days  
Exercisable at end of period 6 years 9 months 7 days    
Vested or expected to vest at end of period 7 years 10 months 2 days    
Aggregate Intrinsic Value      
Outstanding at the beginning of the period $ 6,579    
Outstanding at the end of the period 4,267 $ 6,579  
Exercisable at the end of the period 3,562    
Vested or expected to vest at end of period 4,223    
Unrecognized stock-based compensation expense      
Intrinsic value of options exercised 300 600 $ 100
Fair value of options vested $ 1,400 $ 500 $ 300
Weighted average grant date fair value of options granted (in dollars per share) $ 7.68 $ 4.94 $ 1.66
Options to purchase Common Stock      
Unrecognized stock-based compensation expense      
Unrecognized compensation expense related to unvested stock option awards $ 4,800 $ 300  
Weighted-average amortization period over which cost is expected to be recognized 2 years 10 months 24 days