Regulatory Matters (Details) $ in Millions	6 Months Ended
	Mar. 31, 2017 USD ($)
Regulatory Matters [Line Items]
Amount of requested increase to annual revenues	$ 41.7
Recommended rate increase to annual revenues	$ 8.5
Recommended Equity Ratio	42.30%
Recommended Cost of Equity	8.60%
Approved Rate Increase	$ 5.9
Approved Cost of Equity	8.70%
Approved Equity Ratio	42.90%
Empire [Member]
Regulatory Matters [Line Items]
Depreciation Rate	2.50%
Revenue Sharing Mechanism Level	$ 73.5
Empire [Member] | Maximum [Member]
Regulatory Matters [Line Items]
Estimated Reduction in Annual Revenues	4.0
Empire [Member] | Minimum [Member]
Regulatory Matters [Line Items]
Estimated Reduction in Annual Revenues	$ 3.0
Rate Settlement [Member] | Empire [Member]
Regulatory Matters [Line Items]
Depreciation Rate	2.00%
November 1, 2015 [Member] | Supply Corporation [Member]
Regulatory Matters [Line Items]
Reduction in Rates	2.00%
November 1, 2016 [Member] | Supply Corporation [Member]
Regulatory Matters [Line Items]
Reduction in Rates	2.00%