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Other - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Nov. 07, 2018
Aug. 15, 2018
May 15, 2018
Feb. 15, 2018
Sep. 30, 2018
Sep. 30, 2018
Sep. 30, 2017
Other [Line Items]              
Dividend paid           $ 2,405 $ 1,855
Dividend Paid              
Other [Line Items]              
Dividend paid   $ 900 $ 900 $ 600      
Dividend declared, date of record   Aug. 01, 2018 May 01, 2018 Feb. 01, 2018      
Dividend payable         $ 900 $ 900  
Dividend payable date         Nov. 15, 2018    
Dividend Declared | Subsequent Event              
Other [Line Items]              
Dividend declared, date of record Feb. 01, 2019            
Dividend payable date Feb. 15, 2019            
Quarterly dividend declared $ 0.0425