Retirement Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Retirement benefits expense under the provisions of the plan	$ 290,000	$ 282,000

Amount of cost (reversal of cost) for pension and other postretirement benefits.

No definition available.

Name:	us-gaap_PensionAndOtherPostretirementBenefitExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration