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Note 9 - Employee Benefit Plans - Allocation of Plans' Assets (Details) - USD ($) | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
--- | --- | --- | ---
Pension Plan [Member] |  |  |
Asset | $ 26,878,661 | $ 28,017,797 | $ 38,914,107
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 10,431,848 | 28,017,797 |
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 16,446,813 | 0 |
Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Other Postretirement Benefits Plan [Member] |  |  |
Asset | 13,019,313 | 12,138,119 | $ 15,882,342
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 13,019,313 | 12,138,119 |
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | $ 0 | $ 0 |
Defined Benefit Plan, Equity Securities [Member] |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 29.00% |
Defined Benefit Plan, Equity Securities [Member] | Pension Plan [Member] |  |  |
Target | 25.00% | 30.00% |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage | 27.00% | 13.00% |
Defined Benefit Plan, Equity Securities [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Target | 30.00% | 50.00% |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage | 43.00% | 48.00% |
Defined Benefit Plan, Debt Security [Member] |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 70.00% |
Defined Benefit Plan, Debt Security [Member] | Pension Plan [Member] |  |  |
Target | 75.00% |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage | 72.00% | 0.00% |
Defined Benefit Plan, Debt Security [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Target | 70.00% |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage | 37.00% | 51.00% |
Defined Benefit Plan, Cash [Member] |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 1.00% |
Defined Benefit Plan, Cash [Member] | Pension Plan [Member] |  |  |
Target | 0.00% |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage | 1.00% | 87.00% |
Asset | $ 202,218 | $ 24,312,969 |
Defined Benefit Plan, Cash [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 202,218 | 24,312,969 |
Defined Benefit Plan, Cash [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Cash [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | $ 0 | $ 0 |
Defined Benefit Plan, Cash [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Target | 0.00% |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage | 20.00% | 1.00% |
Asset | $ 2,640,622 | $ 75,219 |
Defined Benefit Plan, Cash [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 2,640,622 | 75,219 |
Defined Benefit Plan, Cash [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Cash [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Common Collective Trust And Pooled Fund Bonds, Liability Driven Investment [Member] | Pension Plan [Member] |  |  |
Asset | 16,446,813 |  |
Defined Benefit Plan, Common Collective Trust And Pooled Fund Bonds, Liability Driven Investment [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Common Collective Trust And Pooled Fund Bonds, Liability Driven Investment [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 16,446,813 |  |
Defined Benefit Plan, Common Collective Trust And Pooled Fund Bonds, Liability Driven Investment [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Pension Plan [Member] |  |  |
Asset | 2,256,767 | 1,172,296 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 2,256,767 | 1,172,296 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 1,693,422 | 1,698,421 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 1,693,422 | 1,698,421 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Mutual Fund Bonds, Domestic Fixed Income [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 4,841,048 | 5,644,954 |
Defined Benefit Plan, Mutual Fund Bonds, Domestic Fixed Income [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 4,841,048 | 5,644,954 |
Defined Benefit Plan, Mutual Fund Bonds, Domestic Fixed Income [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Mutual Fund Bonds, Domestic Fixed Income [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Mutual Fund [Member] | Pension Plan [Member] |  |  |
Asset | 3,000,525 |  |
Mutual Fund [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 3,000,525 |  |
Mutual Fund [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 |  |
Mutual Fund [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Pension Plan [Member] |  |  |
Asset | 2,222,733 | 1,172,714 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 2,222,733 | 1,172,714 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 1,570,538 | 1,793,746 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 1,570,538 | 1,793,746 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Mutual Fund Bonds, Foreign Fixed Income [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset |  | 589,284 |
Defined Benefit Plan, Mutual Fund Bonds, Foreign Fixed Income [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset |  | 589,284 |
Defined Benefit Plan, Mutual Fund Bonds, Foreign Fixed Income [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Mutual Fund Bonds, Foreign Fixed Income [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] |  |  |
Asset |  | 486,184 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset |  | 486,184 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 433,886 | 469,659 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 433,886 | 469,659 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Mutual Funds, Foreign Large Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Pension Plan [Member] |  |  |
Asset | 721,588 | 873,634 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 721,588 | 873,634 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 724,535 | 574,996 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 724,535 | 574,996 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Core [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Pension Plan [Member] |  |  |
Asset | 1,082,801 |  |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 1,082,801 |  |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 588,898 | 443,900 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 588,898 | 443,900 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Core [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Growth [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset |  | 182,823 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset |  | 182,823 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Growth [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Equity Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] |  |  |
Asset | 481,309 |  |
Defined Benefit Plan, Equity Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 481,309 |  |
Defined Benefit Plan, Equity Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Mutual Funds, Foreign Large Cap Growth [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Pension Plan [Member] |  |  |
Asset | 463,907 |  |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 463,907 |  |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | 0 |  |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset | 526,364 | 462,196 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset | 526,364 | 462,196 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset | 0 | 0 |
Defined Benefit Plan, Equity Funds, Foreign Large Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset | $ 0 | 0 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Value [Member] | Other Postretirement Benefits Plan [Member] |  |  |
Asset |  | 202,921 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Asset |  | 202,921 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Asset |  | 0 |
Defined Benefit Plan, Equity Funds, Domestic Small/Mid Cap Value [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Asset |  | $ 0 |

X
- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + 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)(02) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -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 4: 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 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -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 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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