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Other - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Nov. 07, 2017
Aug. 15, 2017
May 15, 2017
Feb. 15, 2017
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Other [Line Items]                
Cash dividend paid             $ 1,855,000 $ 1,804,000
Quarterly dividend declared         $ 0.0425 $ 0.0425 $ 0.1275 $ 0.1275
Dividend Paid                
Other [Line Items]                
Cash dividend paid   $ 619,000 $ 613,000 $ 613,000        
Dividend declared, date of record   Aug. 01, 2017 May 01, 2017 Feb. 01, 2017        
Dividend payable         $ 638,000   $ 638,000  
Dividend payable date         Nov. 15, 2017      
Dividend Declared | Subsequent Event                
Other [Line Items]                
Dividend declared, date of record Feb. 01, 2018              
Dividend payable date Feb. 15, 2018              
Dividend declaration date Nov. 07, 2017              
Quarterly dividend declared $ 0.0425