Summary of Significant Accounting Policies (Narrative) (Details) $ / shares in Units, customer in Thousands	12 Months Ended
	Sep. 30, 2020 USD ($) pipeline customer instrument_held debt_instrument	Sep. 30, 2019 USD ($) instrument_held $ / shares	Oct. 01, 2019 USD ($) lease	Jun. 30, 2019 USD ($)	Jun. 30, 2019	Jun. 30, 2019 instrument_held	Jun. 30, 2019 debt_instrument
Summary Of Significant Accounting Policies [Line Items]
Number of customers | customer	62
Amortization	$ 1,106,511	$ 368,011
Remaining amount of regulatory assets that did not earn a return during the recovery period	$ 13,803,616
Regulatory utility assets provision, review period	5 years
Composite weighted-average depreciation rate	3.30%	3.31%
Effect of change in deprecation rate on depreciation expense		$ (32,570)
Effect of change in depreciation rate on net income		$ 24,187
Effect of change in deprecation rate on EPS (in usd per share) | $ / shares		$ 0.01
Capitalized debt financing costs	$ 81,629
Capitalized equity financing costs	248,579
Unbilled revenue	$ 1,041,518	$ 1,236,384
Deferred charges, amortization period	12 months
Number of pipelines | pipeline	2
Change in accrued capital calls	$ 2,512,387	$ 5,117,942
Number of operating lease | lease			1
Quarterly lease payments			$ 3,240
Roanoke Gas | Unsecured Debt | Unsecured term note payable, at 30-day LIBOR plus 0.90%, November 1, 2021
Summary Of Significant Accounting Policies [Line Items]
Debt instrument, face amount	$ 7,000,000
Fixed rate related to interest rate swap	2.30%
RGC Midstream, LLC
Summary Of Significant Accounting Policies [Line Items]
Number of notes	2					2	2
RGC Midstream, LLC | Unsecured Debt | Unsecured term note payable, at 30-day LIBOR plus 1.15%, due June 12, 2026
Summary Of Significant Accounting Policies [Line Items]
Debt instrument, face amount				$ 14,000,000
Fixed rate related to interest rate swap					3.24%
RGC Midstream, LLC | Unsecured Debt | Unsecured term note payable, at 30-day LIBOR plus 1.20%, due June 1, 2024
Summary Of Significant Accounting Policies [Line Items]
Debt instrument, face amount				$ 10,000,000
Fixed rate related to interest rate swap					3.14%
Natural Gas
Summary Of Significant Accounting Policies [Line Items]
Number of derivative instruments | instrument_held	0	0
Interest Rate Swap
Summary Of Significant Accounting Policies [Line Items]
Number of derivative instruments | instrument_held	3