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Stock Options - Summary of Outstanding Stock Option Activity (Details) - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Number of shares, Beginning balance 1,407,049  
Number of shares, Granted 395,485  
Number of shares, Exercised (77,994)  
Number of shares, Expired/Forfeited (63,891)  
Number of shares, Ending balance 1,660,649 1,407,049
Number of shares, Vested and exercisable 645,179  
Number of shares, Vested and expected to vest 1,660,649  
Weighted average exercise price, Beginning balance $ 8.73  
Weighted average exercise price, Granted 11.39  
Weighted average exercise price, Exercised 2.96  
Weighted average exercise price, Expired/Forfeited 11.19  
Weighted average exercise price, Ending balance 9.54 $ 8.73
Weighted average exercise price, Vested and exercisable 7.97  
Weighted average exercise price, Vested and expected to vest $ 9.54  
Weighted average remaining contractual term 8 years 3 months 18 days 8 years 1 month 6 days
Weighted average remaining contractual term, Granted 9 years 6 months  
Weighted average remaining contractual term, Exercised 4 years 6 months  
Weighted average remaining contractual term, Expired/Forfeited 1 month 6 days  
Weighted average remaining contractual term, Vested and exercisable 7 years 2 months 12 days  
Weighted average remaining contractual term, Vested and expected to vest 8 years 3 months 18 days