Income Taxes (Narrative) (Details) (USD $)	6 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Sep. 30, 2013
Income Taxes [Line Items]
Tax benefit recorded from exercise of stock options	$ 3,100,000		$ 700,000
Tax Benefit Not Realized Due to Tax Loss Carryforward	36,400,000		36,400,000
Taxes refundable to customers	90,779,000		85,655,000
Recoverable future taxes	161,258,000		163,355,000
Amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate	2,000,000
Change in unrecognized tax benefits	2,000,000
Tax benefit from change in enacted rate	(21,829,000)	(19,769,000)
Deferred Income Taxes [Member]
Income Taxes [Line Items]
Taxes refundable to customers	90,800,000		85,700,000
Recoverable future taxes	161,300,000		163,400,000
State Tax Law Change [Member]
Income Taxes [Line Items]
Tax benefit from change in enacted rate	$ 2,800,000
New York State | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Corporate Tax Rate	7.10%
Effective January 1, 2016 [Member] | New York State | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Corporate Tax Rate	6.50%