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Note 12 - Employee Benefit Plans (Tables) | 12 Months Ended
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Sep. 30, 2025
Notes Tables |
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan [Table Text Block] |
|  | Pension Plan |  |  | Postretirement Plan |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Accumulated benefit obligation |  | $ | 26,298,490 |  |  | $ | 26,859,162 |  |  | $ | 10,462,318 |  |  | $ | 10,842,455 |
Change in benefit obligation: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Benefit obligation at beginning of year |  | $ | 29,873,428 |  |  | $ | 26,747,624 |  |  | $ | 10,842,455 |  |  | $ | 11,248,448 |
Service cost |  |  | 387,429 |  |  |  | 324,265 |  |  |  | 4,376 |  |  |  | 30,398 |
Interest cost |  |  | 1,410,406 |  |  |  | 1,468,822 |  |  |  | 507,423 |  |  |  | 613,477 |
Actuarial loss (gain) |  |  | (752,215 | ) |  |  | 2,613,621 |  |  |  | (297,327 | ) |  |  | (540,914 | )
Benefit payments, net of retiree contributions |  |  | (1,439,028 | ) |  |  | (1,280,904 | ) |  |  | (594,609 | ) |  |  | (508,954 | )
Benefit obligation at end of year |  | $ | 29,480,020 |  |  | $ | 29,873,428 |  |  | $ | 10,462,318 |  |  | $ | 10,842,455 |
Change in fair value of plan assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of plan assets at beginning of year |  | $ | 31,054,138 |  |  | $ | 26,878,661 |  |  | $ | 15,078,281 |  |  | $ | 13,019,313 |
Actual return on plan assets, net of taxes |  |  | 872,291 |  |  |  | 5,456,381 |  |  |  | 907,150 |  |  |  | 2,567,922 |
Employer contributions |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Benefit payments, net of retiree contributions |  |  | (1,439,028 | ) |  |  | (1,280,904 | ) |  |  | (594,609 | ) |  |  | (508,954 | )
Fair value of plan assets at end of year |  | $ | 30,487,401 |  |  | $ | 31,054,138 |  |  | $ | 15,390,822 |  |  | $ | 15,078,281 |
Funded status |  | $ | 1,007,381 |  |  | $ | 1,180,710 |  |  | $ | 4,928,504 |  |  | $ | 4,235,826 |
Amounts recognized in the consolidated balance sheet consist of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Benefit plan assets under other non-current assets |  | $ | 1,007,381 |  |  | $ | 1,180,710 |  |  | $ | 4,928,504 |  |  | $ | 4,235,826 |
Amounts recognized in accumulated other comprehensive income: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net actuarial loss (gain), net of tax |  | $ | 923,823 |  |  | $ | 432,149 |  |  | $ | (520,987 | ) |  | $ | (227,071 | )
Total amounts included in accumulated other comprehensive income, net of tax |  | $ | 923,823 |  |  | $ | 432,149 |  |  | $ | (520,987 | ) |  | $ | (227,071 | )
Amounts deferred to a regulatory asset (liability): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net actuarial loss (gain) |  | $ | 2,199,542 |  |  | $ | 3,041,666 |  |  | $ | (3,879,294 | ) |  | $ | (4,032,929 | )
Amounts recognized as regulatory assets (liabilities) |  | $ | 2,199,542 |  |  | $ | 3,041,666 |  |  | $ | (3,879,294 | ) |  | $ | (4,032,929 | )
Defined Benefit Plan, Assumptions [Table Text Block] |
|  | Pension Plan |  |  | Postretirement Plan |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Assumptions used to determine benefit obligations: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate |  |  | 5.29 | % |  |  | 4.83 | % |  |  | 5.16 | % |  |  | 4.83 | %
Expected rate of compensation increase |  |  | 4.00 | % |  |  | 4.00 | % |  |  | N/A |  |  |  | N/A |
Assumptions used to determine benefit costs: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate |  |  | 4.83 | % |  |  | 5.63 | % |  |  | 4.83 | % |  |  | 5.63 | %
Expected long-term rate of return on plan assets |  |  | 4.95 | % |  |  | 4.50 | % |  |  | 4.95 | % |  |  | 4.21 | %
Expected rate of compensation increase |  |  | 4.00 | % |  |  | 4.00 | % |  |  | N/A |  |  |  | N/A |
Schedule of Net Benefit Costs [Table Text Block] |
|  | Pension Plan |  |  | Postretirement Plan |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Service cost |  | $ | 387,429 |  |  | $ | 324,265 |  |  | $ | 4,376 |  |  | $ | 30,398 |
Interest cost |  |  | 1,410,406 |  |  |  | 1,468,822 |  |  |  | 507,423 |  |  |  | 613,477 |
Expected return on plan assets |  |  | (1,503,902 | ) |  |  | (1,179,830 | ) |  |  | (729,708 | ) |  |  | (533,249 | )
Recognized loss (gain) |  |  | 59,423 |  |  |  | 316,522 |  |  |  | (232,611 | ) |  |  | (40,597 | )
Net periodic benefit cost (income) |  | $ | 353,356 |  |  | $ | 929,779 |  |  | $ | (450,520 | ) |  | $ | 70,029 |
Schedule of Health Care Cost Trend Rates [Table Text Block] |
|  | Pre 65 |  |  | Post 65 |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Health care cost trend rate assumed for next year |  |  | 7.00 | % |  |  | 7.00 | % |  |  | 5.60 | % |  |  | 5.60 | %
Rate to which the cost trend is assumed to decline (the ultimate trend rate) |  |  | 4.00 | % |  |  | 4.00 | % |  |  | 4.00 | % |  |  | 4.00 | %
Year that the rate reaches the ultimate trend rate |  | 2075 |  |  | 2075 |  |  | 2075 |  |  | 2075 |
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block] |
|  | 1% Increase |  |  | 1% Decrease |
Effect on total service and interest cost components |  | $ | 58,000 |  |  | $ | (50,000 | )
Effect on accumulated postretirement benefit obligation |  |  | 1,113,000 |  |  |  | (955,000 | )
Schedule of Allocation of Plan Assets [Table Text Block] |
|  | Pension Plan |  |  | Postretirement Plan |
|  | Target |  |  | 2025 |  |  | 2024 |  |  | Target |  |  | 2025 |  |  | 2024 |
Asset category: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity securities |  |  | 25 | % |  |  | 23 | % |  |  | 25 | % |  |  | 30 | % |  |  | 38 | % |  |  | 48 | %
Debt securities |  |  | 75 | % |  |  | 77 | % |  |  | 75 | % |  |  | 70 | % |  |  | 53 | % |  |  | 36 | %
Cash |  |  | — | % |  |  | — | % |  |  | — | % |  |  | — | % |  |  | 9 | % |  |  | 16 | %
|  |  |  |  |  | Pension Plan |
|  |  |  |  |  | Fair Value Measurements - September 30, 2025 |
|  | Fair Value |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Asset Class: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash |  | $ | 27,603 |  |  | $ | 27,603 |  |  | $ | — |  |  | $ | — |
Common and Collective Trust and Pooled Funds: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bond Funds |  |  | 19,460,378 |  |  |  | — |  |  |  | 19,460,378 |  |  |  | — |
Mutual Funds: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Fixed Income |  |  | 3,901,202 |  |  |  | 3,901,202 |  |  |  | — |  |  |  | — |
Equities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Large Cap Growth |  |  | 2,161,688 |  |  |  | 2,161,688 |  |  |  | — |  |  |  | — |
Domestic Large Cap Value |  |  | 2,470,055 |  |  |  | 2,470,055 |  |  |  | — |  |  |  | — |
Domestic Small/Mid Cap Core |  |  | 1,023,627 |  |  |  | 1,023,627 |  |  |  | — |  |  |  | — |
Foreign Large Cap Growth |  |  | 442,847 |  |  |  | 442,847 |  |  |  | — |  |  |  | — |
Foreign Large Cap Value |  |  | 469,821 |  |  |  | 469,821 |  |  |  | — |  |  |  | — |
Foreign Large Cap Core |  |  | 530,180 |  |  |  | 530,180 |  |  |  | — |  |  |  | — |
Total |  | $ | 30,487,401 |  |  | $ | 11,027,023 |  |  | $ | 19,460,378 |  |  | $ | — |
|  |  |  |  |  | Pension Plan |
|  |  |  |  |  | Fair Value Measurements - September 30, 2024 |
|  | Fair Value |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Asset Class: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash |  | $ | 142,921 |  |  | $ | 142,921 |  |  | $ | — |  |  | $ | — |
Common and Collective Trust and Pooled Funds: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bond Funds |  |  | 19,505,237 |  |  |  | — |  |  |  | 19,505,237 |  |  |  | — |
Mutual Funds: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Fixed Income |  |  | 3,791,697 |  |  |  | 3,791,697 |  |  |  | — |  |  |  | — |
Equities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Large Cap Growth |  |  | 2,073,092 |  |  |  | 2,073,092 |  |  |  | — |  |  |  | — |
Domestic Large Cap Value |  |  | 2,469,045 |  |  |  | 2,469,045 |  |  |  | — |  |  |  | — |
Domestic Small/Mid Cap Core |  |  | 1,297,579 |  |  |  | 1,297,579 |  |  |  | — |  |  |  | — |
Foreign Large Cap Growth |  |  | 498,732 |  |  |  | 498,732 |  |  |  | — |  |  |  | — |
Foreign Large Cap Value |  |  | 482,222 |  |  |  | 482,222 |  |  |  | — |  |  |  | — |
Foreign Large Cap Core |  |  | 793,613 |  |  |  | 793,613 |  |  |  | — |  |  |  | — |
Total |  | $ | 31,054,138 |  |  | $ | 11,548,901 |  |  | $ | 19,505,237 |  |  | $ | — |
|  |  |  |  |  | Postretirement Plan |
|  |  |  |  |  | Fair Value Measurements - September 30, 2025 |
|  | Fair Value |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Asset Class: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash |  | $ | 1,462,600 |  |  | $ | 1,462,600 |  |  | $ | — |  |  | $ | — |
Mutual Funds: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Fixed Income |  |  | 8,089,514 |  |  |  | 8,089,514 |  |  |  | — |  |  |  | — |
Equities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Large Cap Growth |  |  | 1,340,584 |  |  |  | 1,340,584 |  |  |  | — |  |  |  | — |
Domestic Large Cap Value |  |  | 2,799,537 |  |  |  | 2,799,537 |  |  |  | — |  |  |  | — |
Domestic Small/Mid Cap Core |  |  | 453,828 |  |  |  | 453,828 |  |  |  | — |  |  |  | — |
Foreign Large Cap Growth |  |  | 217,707 |  |  |  | 217,707 |  |  |  | — |  |  |  | — |
Foreign Large Cap Core |  |  | 1,027,052 |  |  |  | 1,027,052 |  |  |  | — |  |  |  | — |
Total |  | $ | 15,390,822 |  |  | $ | 15,390,822 |  |  | $ | — |  |  | $ | — |
|  |  |  |  |  | Postretirement Plan |
|  |  |  |  |  | Fair Value Measurements - September 30, 2024 |
|  | Fair Value |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Asset Class: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash |  | $ | 2,381,909 |  |  | $ | 2,381,909 |  |  | $ | — |  |  | $ | — |
Mutual Funds: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Fixed Income |  |  | 5,457,976 |  |  |  | 5,457,976 |  |  |  | — |  |  |  | — |
Equities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic Large Cap Growth |  |  | 2,412,824 |  |  |  | 2,412,824 |  |  |  | — |  |  |  | — |
Domestic Large Cap Value |  |  | 1,996,262 |  |  |  | 1,996,262 |  |  |  | — |  |  |  | — |
Domestic Small/Mid Cap Core |  |  | 738,393 |  |  |  | 738,393 |  |  |  | — |  |  |  | — |
Foreign Large Cap Growth |  |  | 532,391 |  |  |  | 532,391 |  |  |  | — |  |  |  | — |
Foreign Large Cap Value |  |  | 652,023 |  |  |  | 652,023 |  |  |  | — |  |  |  | — |
Foreign Large Cap Core |  |  | 906,503 |  |  |  | 906,503 |  |  |  | — |  |  |  | — |
Total |  | $ | 15,078,281 |  |  | $ | 15,078,281 |  |  | $ | — |  |  | $ | — |
Schedule of Expected Benefit Payments [Table Text Block] |
|  |  | Pension |  |  | Postretirement |
Fiscal year ending September 30 |  |  | Plan |  |  | Plan |
2026 |  |  | $ | 1,463,000 |  |  | $ | 728,140 |
2027 |  |  |  | 1,560,000 |  |  |  | 753,633 |
2028 |  |  |  | 1,630,000 |  |  |  | 747,643 |
2029 |  |  |  | 1,701,000 |  |  |  | 773,121 |
2030 |  |  |  | 1,780,000 |  |  |  | 760,210 |
2031 - 2035 |  |  |  | 9,733,000 |  |  |  | 3,794,802 |
NQDC Plan [Member] |
Notes Tables |
Defined Contribution Plan Disclosures [Table Text Block] |
|  | 2025 |  |  | 2024 |
Beginning deferred compensation balance |  | $ | 113,600 |  |  | $ | 47,674 |
Employer contributions |  |  | 80,510 |  |  |  | 52,400 |
Earnings |  |  | 7,084 |  |  |  | 13,526 |
Ending deferred compensation balance |  | $ | 201,194 |  |  | $ | 113,600 |
The 401K Plan [Member] |
Notes Tables |
Defined Contribution Plan Disclosures [Table Text Block] |
|  | Years Ended September 30 |
|  | 2025 |  |  | 2024 |
Matching contribution |  | $ | 466,630 |  |  | $ | 427,022 |
Discretionary contribution |  |  | 137,114 |  |  |  | 112,207 |

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