Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	$ 244,911	$ 338,405
Regulatory Liabilities	37,287	28,344
Postretirement benefits [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	16,497	13,147
Environmental overcollections [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	2,552	2,883
Deferred fuel and power refunds [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	8,283	4,435
State tax benefits - distribution system repairs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	8,453	7,385
Other [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	1,502	494
Income taxes recoverable [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	106,069	103,172
Underfunded pension and postretirement plans [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	94,515	188,222
Environmental costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	17,054	16,812
Deferred fuel and power costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	8,283	11,602
Removal costs, net [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	13,333	12,718
Other [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	$ 5,657	$ 5,879