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Stock Options - Summary of Outstanding Stock Option Activity (Details) - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Number of shares, Beginning balance 1,040,387 756,692 504,550  
Number of shares, Granted 471,144 359,319 512,402  
Number of shares, Exercised (284,455) (58,155) (24,260)  
Number of shares, Expired/Forfeited (23,449) (17,469) (236,000)  
Number of shares, Ending balance 1,203,627 1,040,387 756,692 504,550
Number of shares, Vested and exercisable 523,566      
Number of shares, Vested and expected to vest 1,203,627      
Weighted average exercise price, Beginning balance $ 2.25 $ 2.10 $ 2.60  
Weighted average exercise price, Granted 14.72 2.60 2.00  
Weighted average exercise price, Exercised 2.07 2.36 3.19  
Weighted average exercise price, Expired/Forfeited 8.22 2.13 2.77  
Weighted average exercise price, Ending balance 7.06 $ 2.25 $ 2.10 $ 2.60
Weighted average exercise price, Vested and exercisable 2.21      
Weighted average exercise price, Vested and expected to vest $ 7.06      
Weighted average remaining contractual term 8 years 1 month 6 days 7 years 9 months 18 days 7 years 7 months 6 days 5 years 9 months 18 days
Weighted average remaining contractual term, Granted 5 years 2 months 12 days 9 years 4 months 24 days 9 years 2 months 12 days  
Weighted average remaining contractual term, Exercised 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