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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
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-Section 55
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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
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