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Share-Based Payment Awards - Stock Options - Additional Information (Detail) - shares
1 Months Ended 9 Months Ended
Jan. 31, 2019
Sep. 30, 2019
2016 Long Term Incentive Plan [Member]    
Class of Stock [Line Items]    
Ratable monthly vesting period 4 years  
Contractual life of option grants 10 years  
Stock Compensation Plan [Member]    
Class of Stock [Line Items]    
Ratable monthly vesting period 1 year  
Cliff vesting period 3 years  
Common stock vested during the period   1,839,397
Newly Appointed Non Executive Director [Member]    
Class of Stock [Line Items]    
Ratable annual vesting period 3 years  
External consultant [Member]    
Class of Stock [Line Items]    
Cliff vesting period 1 year