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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Income Taxes [Line Items]
Effective tax rate (ETR) from continuing operations	24.90%	40.90%	25.30%	27.60%
Statutory federal tax rate				21.00%
State net operating loss carryforwards					$ 0.7
Domestic Tax Authority [Member] | 2027-2038 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards					512.4
State and Local Jurisdiction [Member] | 2021-2040 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards					$ 223.9
Minimum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2027
Minimum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2021
Maximum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2038
Maximum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2040

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Income Taxes [Line Items]

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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