Income Taxes - Expiration Dates of NOLs and Other Tax Credit Carryforwards Before Valuation Allowances (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2021
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2029
Minimum [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2022
Maximum [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2028