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Stock Options - Summary of Outstanding Stock Option Activity (Details) - $ / shares
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Number of shares, Beginning balance 1,203,627 1,040,387 756,692  
Number of shares, Granted 1,009,134 471,144 359,319  
Number of shares, Exercised (341,456) (284,455) (58,155)  
Number of shares, Expired/Forfeited (464,256) (23,449) (17,469)  
Number of shares, Ending balance 1,407,049 1,203,627 1,040,387 756,692
Number of shares, Vested and exercisable 504,287      
Number of shares, Vested and expected to vest 1,407,049      
Weighted average exercise price, Beginning balance $ 7.06 $ 2.25 $ 2.10  
Weighted average exercise price, Granted 9.94 14.72 2.60  
Weighted average exercise price, Exercised 2.24 2.07 2.36  
Weighted average exercise price, Expired/Forfeited 11.81 8.22 2.13  
Weighted average exercise price, Ending balance 8.73 $ 7.06 $ 2.25 $ 2.10
Weighted average exercise price, Vested and exercisable 6.28      
Weighted average exercise price, Vested and expected to vest $ 8.73      
Weighted average remaining contractual term 8 years 1 month 6 days 8 years 1 month 6 days 7 years 9 months 18 days 7 years 7 months 6 days
Weighted average remaining contractual term, Granted 6 years 9 months 18 days 9 years 1 month 6 days 9 years 4 months 24 days  
Weighted average remaining contractual term, Exercised 1 year 3 months 18 days 5 years 2 months 12 days 3 years 6 months  
Weighted average remaining contractual term, Expired/Forfeited     2 years 7 months 6 days  
Weighted average remaining contractual term, Vested and exercisable 7 years      
Weighted average remaining contractual term, Vested and expected to vest 8 years 1 month 6 days