Regulatory Matters (Details) $ in Millions	3 Months Ended
	Dec. 31, 2015 USD ($)
Regulatory Matters [Line Items]
Rate proceeding refund provision pre tax	$ 7.5
Allowed rate of return on equity	9.10%
Authorized Increase in Distribution Corporation's pipeline relacement spending	$ 8.2
Maximum [Member]
Regulatory Matters [Line Items]
Allowed rate of return on equity range	10.50%
Minimum [Member]
Regulatory Matters [Line Items]
Allowed rate of return on equity range	9.50%
9.5 Percent To 10.5 Percent Rate Of Return On Equity [Member] | Shareholder Allocation [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	50.00%
9.5 Percent To 10.5 Percent Rate Of Return On Equity [Member] | Deferred For The Benefit Of Customers [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	50.00%
Above 10.5 Percent Rate Of Return On Equity [Member] | Shareholder Allocation [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	20.00%
Above 10.5 Percent Rate Of Return On Equity [Member] | Deferred For The Benefit Of Customers [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	80.00%
Supply Corporation [Member] | November 1, 2015 [Member]
Regulatory Matters [Line Items]
Reduction in Rates	2.00%
Supply Corporation [Member] | November 1, 2016 [Member]
Regulatory Matters [Line Items]
Reduction in Rates	2.00%