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Note 12 - Employee Benefit Plans - Assumed Health Care Cost Trend Rates (Details)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Pre 65 [Member]
Health care cost trend rate assumed for next year	7.00%	6.30%
Rate to which the cost trend is assumed to decline (the ultimate trend rate)	4.00%	3.94%
Year that the rate reaches the ultimate trend rate	2075	2075
Post 65 [Member]
Health care cost trend rate assumed for next year	5.60%	5.20%
Rate to which the cost trend is assumed to decline (the ultimate trend rate)	4.00%	3.94%
Year that the rate reaches the ultimate trend rate	2075	2075

X

- Definition

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Year ultimate health care cost trend rate is expected to be reached, in YYYY format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanYearHealthCareCostTrendRateReachesUltimateTrendRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:gYearListItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=rgco_Pre65Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=rgco_Post65Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: