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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 |

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