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Note 9 - Fair Value Measurements (Details Textual) Pure in Thousands | Jun. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Customer Concentration Risk [Member] | Accounts Receivable [Member] |  |
Number of Major Customers | 0 | 0

X
- Definition Represents the number of major customers accounting for 5% or more of the specified concentration risk benchmark, which includes, but not limited to, sales revenue, accounts receivable, etc. + References No definition available. + Details
Name: | rgco_NumberOfMajorCustomers
Namespace Prefix: | rgco_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |