Line-of-Credit (Narrative) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Promissory Notes term	20 years
Line-of-credit, maximum borrowing limit	$ 19,000,000
Interest rate on unused line-of-credit (as a percent)	0.15%	0.15%
Debt covenant, maximum ratio of total long-term debt to total capitalization	65.00%
Roanoke Gas | Line of Credit | Line-of-credit, at 30-day LIBOR plus 1.00%, due March 31, 2022
Debt Instrument [Line Items]
Promissory Notes term	2 years
Line-of-credit, maximum borrowing limit	$ 28,000,000
Interest rate on unused line-of-credit (as a percent)	0.15%
Minimum interest coverage ratio	1.5
Debt covenant, maximum ratio of total long-term debt to total capitalization	65.00%
Roanoke Gas | Line of Credit | Line-of-credit, at 30-day LIBOR plus 1.00%, due March 31, 2022 | 30-day LIBOR
Debt Instrument [Line Items]
Variable rate basis points (as a percent)	1.00%