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Income Taxes - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Dec. 31, 2017 | Mar. 31, 2019 | Mar. 31, 2018
Income Tax Disclosure [Line Items] |  |  |
Effective tax rate |  | 28.80% | 23.80%
Provisional remeasurement of deferred tax liabilities resulted in an discrete tax benefit |  | $ 0 | $ 11,200,000
Effective income tax rate excluding impact of net deferred tax liability |  | 28.80% | 33.90%
Unrecognized income tax benefits |  | $ 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 Year2019 |  |  |
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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