Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities Associated With Gas Utility and Electric Utility (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013
Regulatory Assets and Liabilities
Regulatory Assets	$ 235,931	$ 244,911	$ 322,329
Regulatory Liabilities	33,148	37,287	56,654
Postretirement benefits
Regulatory Assets and Liabilities
Regulatory Liabilities	17,196	16,497	13,865
Environmental overcollections
Regulatory Assets and Liabilities
Regulatory Liabilities	1,855	2,552	2,980
Deferred fuel and power refunds
Regulatory Assets and Liabilities
Regulatory Liabilities	3,204	8,283	31,209
State tax benefits -- distribution system repairs
Regulatory Assets and Liabilities
Regulatory Liabilities	8,998	8,453	7,900
Other
Regulatory Assets and Liabilities
Regulatory Liabilities	1,895	1,502	700
Income taxes recoverable
Regulatory Assets and Liabilities
Regulatory Assets	106,800	106,069	104,229
Underfunded pension and postretirement plans
Regulatory Assets and Liabilities
Regulatory Assets	90,996	94,515	181,305
Environmental costs
Regulatory Assets and Liabilities
Regulatory Assets	14,544	17,054	16,841
Deferred fuel and power costs
Regulatory Assets and Liabilities
Regulatory Assets	4,308	8,283	2,122
Removal costs, net
Regulatory Assets and Liabilities
Regulatory Assets	14,379	13,333	11,856
Other
Regulatory Assets and Liabilities
Regulatory Assets	$ 4,904	$ 5,657	$ 5,976