Regulatory Matters (Details) $ in Millions	9 Months Ended
	Jun. 30, 2019 USD ($)
Regulatory Matters [Line Items]
Approved Return on Equity	8.70%
Supply Corporation [Member]
Regulatory Matters [Line Items]
Proposed Annual Cost of Service	$ 295.4
Proposed Rate Base	$ 970.8
Proposed Return on Equity	15.00%
Empire [Member]
Regulatory Matters [Line Items]
Estimated Increase to Revenues from Interim Rates	$ 4.6
Empire [Member] | Maximum [Member]
Regulatory Matters [Line Items]
Revenue Sharing Mechanism Percentage	55.00%
Revenue Sharing Mechanism Revenue Level	$ 68.4
Empire [Member] | Minimum [Member]
Regulatory Matters [Line Items]
Revenue Sharing Mechanism Percentage	35.00%
Revenue Sharing Mechanism Revenue Level	$ 64.4