v3.10.0.1
Share-Based Compensation - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Mar. 31, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Executive Officers [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Service period 3 years        
Cash Settled Performance Awards [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of unvested share awards outstanding   1,508,285   1,508,285  
Payments to vested awards       $ 1,000,000  
Cash Settled Performance Awards [Member] | Executive Officers [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of share awards 774,590        
Fair market value of shares $ 2,400,000        
Restricted Shares Total Shareholder Return Performance Stock Awards [Member] | Executive Officers [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of share awards 387,295        
Fair market value of shares $ 800,000        
Cash Settled Performance Shares [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share-based compensation, current liability   $ 1,100,000   1,100,000  
Share-based compensation, non-current liability   800,000   800,000  
Cash Settled Performance Shares [Member] | General and Administrative Expenses [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share-based compensation expense   $ 27,000 $ 200,000 $ 800,000 $ 500,000