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Stock-Based Compensation (Restricted Stock Awards) - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 9 Months Ended
May 31, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Retained income dividends cumulatively paid $ 1,727 $ 98   $ 1,825    
General and Administrative Expense [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Retained income dividends cumulatively paid 1,346 80   1,426    
Other Operating Income (Expense) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Retained income dividends cumulatively paid $ 381 18   399    
Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Recognized compensation expenses   1,231 $ 1,144 2,890 $ 3,134  
Total unrecognized compensation expense, Nonvested restricted stock arrangements granted   $ 12,597   $ 12,597   $ 9,101
Recognition of remaining compensation expense over a weighted-average period       2 years 10 months 24 days