Regulatory Matters (Details) $ in Millions	6 Months Ended
	Mar. 31, 2016 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
Amount of requested increase to annual revenues	$ 41.7
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%
Shareholder Allocation [Member] | 9.5 Percent To 10.5 Percent Rate Of Return On Equity [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	50.00%
Shareholder Allocation [Member] | Above 10.5 Percent Rate Of Return On Equity [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	20.00%
Deferred For The Benefit Of Customers [Member] | 9.5 Percent To 10.5 Percent Rate Of Return On Equity [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	50.00%
Deferred For The Benefit Of Customers [Member] | Above 10.5 Percent Rate Of Return On Equity [Member]
Regulatory Matters [Line Items]
Earnings sharing mechanism allocation of earnings	80.00%