Note 12 - Employee Benefit Plans - Effect of 1% Change on Health Care Trend Rate Assumptions (Details)	12 Months Ended
Sep. 30, 2024 USD ($)
Effect on total service and interest cost components, 1% increase	$ 71,000
Effect on total service and interest cost components, 1% decrease	(61,000)
Effect on accumulated postretirement benefit obligation, 1% increase	1,204,000
Effect on accumulated postretirement benefit obligation, 1% decrease	$ (1,031,000)

Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate.

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Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate.

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