Income Taxes (Narrative) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Taxes [Line Items]
Tax benefit recorded from exercise of stock options	$ 4,600,000	$ 700,000	$ 1,000,000
Tax benefit not realized due to tax loss carryforwards	34,200,000	34,200,000
Taxes Refundable to Customers	91,736,000	85,655,000
Recoverable Future Taxes	163,485,000	163,355,000
Tax Credit Carryforwards	36,000,000
Federal net operating loss, certain annual limitations	10,000,000
Federal net operating loss, excess tax deductions related to stock based compensation	87,000,000
Tax benefit from change in enacted rate	(26,272,000)	(37,569,000)	(32,974,000)
Deferred Income Taxes [Member]
Income Taxes [Line Items]
Taxes Refundable to Customers	91,736,000	85,655,000
Recoverable Future Taxes	163,485,000	163,355,000
Regulatory liabilities	52,600,000	52,600,000
Regulatory assets	85,300,000	82,500,000
Pennsylvania [Member]
Income Taxes [Line Items]
Net operating loss	297,000,000
California [Member]
Income Taxes [Line Items]
Net operating loss	183,000,000
New York [Member]
Income Taxes [Line Items]
Net operating loss	103,000,000
Federal [Member]
Income Taxes [Line Items]
Net operating loss	367,000,000
State Tax Law Change [Member]
Income Taxes [Line Items]
Tax benefit from change in enacted rate	$ 2,800,000
New York [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Corporate Tax Rate	7.10%
Effective January 1, 2016 [Member] | New York [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Corporate Tax Rate	6.50%