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Note 12 - Employee Benefit Plans - Changes in Benefit Plan Liabilities (Details) - NQDC Plan [Member] - USD ($) | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 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

X
- Definition Amount of earnings on deferred contribution plan. + References No definition available. + Details
Name: | rgco_DeferredContributionPlanEarnings
Namespace Prefix: | rgco_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable beyond one year (or the operating cycle, if longer). + References No definition available. + Details
Name: | us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=rgco_NQDCPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |