Condensed Consolidated Statements of Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Revenues	$ 395,901	$ 345,802	$ 669,698	$ 626,443
Costs and expenses:
Cost of sales — gas, fuel and purchased power (excluding depreciation shown below)	212,785	192,770	351,062	349,676
Operating and administrative expenses	52,421	45,749	96,656	86,691
Operating and administrative expenses - related parties	3,012	2,781	4,817	4,906
Taxes other than income taxes	4,684	4,857	8,960	8,984
Depreciation	12,895	12,328	25,648	24,707
Amortization	817	782	1,635	1,466
Other loss (income), net	57	(1,912)	(874)	(3,039)
Total costs and expenses	286,671	257,355	487,904	473,391
Operating income	109,230	88,447	181,794	153,052
Interest expense	9,820	10,677	19,897	21,284
Income before income taxes	99,410	77,770	161,897	131,768
Income taxes	41,151	29,899	66,826	51,229
Net income	$ 58,259	$ 47,871	$ 95,071	$ 80,539