Regulatory Matters (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2015	Sep. 30, 2014
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%