Regulatory Matters (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2016 USD ($)
Regulatory Matters [Line Items]
Amount of requested increase to annual revenues	$ 41.7
Empire [Member]
Regulatory Matters [Line Items]
Depreciation Rate	2.50%
Revenue Sharing Mechanism Level	$ 73.5
Empire [Member] | Rate Settlement [Member]
Regulatory Matters [Line Items]
Depreciation Rate	2.00%
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