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Share-based Compensation - Schedule of Unvested RSUs Activity (Parenthetical) (Detail) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 3 Months Ended
Sep. 05, 2018
Jan. 16, 2019
Mar. 31, 2019
Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Amortization of share based compensation expense     $ 274 $ 165
Restricted Stock Units (RSUs)        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Restricted stock units granted     183,500  
Grant date fair value per share     $ 7.25  
2018 Stock Incentive Plan | Restricted Stock Units (RSUs)        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Restricted stock units granted   183,500    
Grant date fair value per share   $ 7.25    
2018 Stock Incentive Plan | Restricted Stock Units (RSUs) | Minimum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period   3 years    
2018 Stock Incentive Plan | Restricted Stock Units (RSUs) | Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period   4 years    
2018 Stock Incentive Plan | Restricted Stock Units (RSUs) | Executive Officers and Directors        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Restricted stock units granted 1,487,500      
Grant date fair value per share $ 7.69      
Vesting period 3 years      
Gross revenue threshold limit for vesting of grants $ 7,000      
Amortization of share based compensation expense     $ 0  
2018 Stock Incentive Plan | Restricted Stock Units (RSUs) | Executive Officers and Directors | Time-Based Vesting, Year One        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting percentage 33.33%      
Vesting date Jul. 01, 2019      
2018 Stock Incentive Plan | Restricted Stock Units (RSUs) | Executive Officers and Directors | Time-Based Vesting, Year Two        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting percentage 33.33%      
Vesting date Jul. 01, 2020      
2018 Stock Incentive Plan | Restricted Stock Units (RSUs) | Executive Officers and Directors | Time-Based Vesting, Year Three        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting percentage 33.33%      
Vesting date Jul. 01, 2021      
2018 Stock Incentive Plan | Performance Criteria, RSUs        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Restricted stock units granted   90,000