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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Taxes [Line Items]
Operating loss carryforwards, valuation allowance	$ 2.9	$ 3.1
Unrecognized tax benefits if unrecognized, the balance of uncertain tax benefits would impact the effective tax rate	4.9	$ 4.9	$ 4.7
Domestic Tax Authority [Member]
Income Taxes [Line Items]
Net operating loss carryforwards not subject to expiration	$ 130.7
Effective income tax rate reconciliation, at federal statutory income tax rate, percent	80.00%
Domestic Tax Authority [Member] | 2027-2038 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 541.3
State and Local Jurisdiction [Member] | 2021-2041 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 235.7
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	2041

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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 operating loss carryforwards that are not subject to expiration dates.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards that are subject to expiration dates.

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.Fact.4)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

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-Name Accounting Standards Codification
-Topic 235
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The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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