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Note 9 - Employee Benefit Plans (Details Textual) | 12 Months Ended
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Sep. 30, 2024 | Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($)
Defined Benefit Plan, Expected Amortization, Next Fiscal Year |  | $ 64,000 |
Defined Benefit Plan, Expected Amortization Of Net Gains (Losses), Regulatory Deferral |  | 243,000 |
Defined Benefit Plan, Expected Amortization of Net Gains (Losses), Regulatory Deferral Liabilities |  | $ 31,000 |
The 401K Plan [Member] |  |  |
Defined Contribution Plan, Minimum Annual Contributions Per Employee, Percent |  | 1.00% |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent |  | 50.00% |
Defined Contribution Plan, Employer Matching Contribution, Match Percentage |  | 100.00% |
Defined Contribution Plan, Employer Matching Contribution, Percent of 100 Percent Match |  | 4.00% |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match, Second Tranche |  | 50.00% |
Defined Contribution Plan, Employer Matching Contribution, Percent of 50% Match |  | 2.00% |
Defined Benefit Plan, Equity Securities [Member] |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  |  | 29.00%
Defined Benefit Plan, Debt Security [Member] |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  |  | 70.00%
Defined Benefit Plan, Cash [Member] |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  |  | 1.00%
Pension Plan [Member] |  |  |
Defined Benefit Plan, Period Before Benefits are Fully Vested (Year) |  | 5 years |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-Term Rate of Return on Plan Assets |  | 4.50% | 4.75%
Defined Benefit Plan, Plan Assets, Contributions by Employer |  | $ 0 | $ 0
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  | $ 0 |
Pension Plan [Member] | Forecast [Member] |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-Term Rate of Return on Plan Assets | 4.50% |  |
Pension Plan [Member] | Fixed Income Securities [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 75.00% | 70.00%
Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 25.00% | 30.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 27.00% | 13.00%
Pension Plan [Member] | Defined Benefit Plan, Debt Security [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 75.00% |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 72.00% | 0.00%
Pension Plan [Member] | Defined Benefit Plan, Cash [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 0.00% |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 1.00% | 87.00%
Other Postretirement Benefits Plan [Member] |  |  |
Defined Benefit Plan, Minimum Service Requirement (Year) |  | 10 years |
Defined Benefit Plan, Age Requirement |  | 55 |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-Term Rate of Return on Plan Assets |  | 3.95% | 4.24%
Defined Benefit Plan, Plan Assets, Contributions by Employer |  | $ 0 | $ 0
Other Postretirement Benefits Plan [Member] | Forecast [Member] |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-Term Rate of Return on Plan Assets | 4.24% |  |
Other Postretirement Benefits Plan [Member] | Fixed Income Securities [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 70.00% | 50.00%
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 30.00% | 50.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 43.00% | 48.00%
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Debt Security [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 70.00% |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 37.00% | 51.00%
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Cash [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage |  | 0.00% |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 20.00% | 1.00%

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- Definition The age requirement of defined benefit plan. + References No definition available. + Details
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- Definition Amount of cost (credit) included in regulatory deferral expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position. + References No definition available. + Details
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- Definition Amount of expected amortization of net gain (losses) on regulatory deferral liabilities of defined benefit plan. + References No definition available. + Details
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- Definition The minimum period of service required under defined benefit plan. + References No definition available. + Details
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- Definition The period before benefits ae fully vested under defined benefit plan. + References No definition available. + Details
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- Definition The percentage that the employer will match contribution of employee contribution under defined contribution plan. + References No definition available. + Details
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- Definition Percentage employer matches of the employee's percentage contribution matched at 100% match. + References No definition available. + Details
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- Definition Percentage employer matches 50% of the employee's percentage contribution matched. + References No definition available. + Details
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- Definition Represents the employer matching contribution expressed as a percent of match, second tranche. + References No definition available. + Details
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- Definition Minimum percentage of employee gross pay the employee may contribute to a defined contribution plan. + References No definition available. + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of cost (credit) included in accumulated other comprehensive (income) loss expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position. + References 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 + Details
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- Definition Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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