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Income Taxes - Additional Information (Detail) - USD ($)
 3 Months Ended 6 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Income Tax Disclosure [Line Items]        
Tax Cuts and Jobs Act, percentage of depreciation for certain fixed assets acquired     100.00%  
Provisional remeasurement of deferred tax assets and liabilities resulted in an discrete tax benefit   $ 11,500,000    
Decrease in provisional remeasurement amount $ 200,000      
Effective tax rate 33.80%   23.80% 40.90%
Provisional income tax benefit due to reduction in Federal corporate tax rate $ (216,000)   $ 11,236,000  
Effective income tax rate excluding impact of net deferred tax liability     33.90%  
Unrecognized income tax benefits $ 0   $ 0  
Federal        
Income Tax Disclosure [Abstract]        
Number of years for examination     4 years  
Federal | Tax Year 2017        
Income Tax Disclosure [Line Items]        
Corporate income tax rate     35.00%  
Federal | Tax Year 2018        
Income Tax Disclosure [Line Items]        
Corporate income tax rate     21.00%  
New York        
Income Tax Disclosure [Abstract]        
Number of years for examination     4 years  
Connecticut        
Income Tax Disclosure [Abstract]        
Number of years for examination     4 years  
Pennsylvania        
Income Tax Disclosure [Abstract]        
Number of years for examination     4 years  
New Jersey        
Income Tax Disclosure [Abstract]        
Number of years for examination     5 years