Financial Instruments Fair Value Hedges and Cash Flow Hedges (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Effect of Fair Value Hedges on Results of Operations [Abstract]
Commodity contracts	$ 10,311	$ (792)	$ 2,165
Fair value adjustment for natural gas inventory designated as the hedged item	(9,768)	2,486	15,938
Total (increase) decrease in purchased gas cost	543	1,694	18,103
Fair Value Hedge Basis Ineffectiveness	811	(919)	(208)
Fair Value Hedge Timing Ineffectiveness	(268)	2,613	18,311
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	(41,716)	8,365	(10,778)
Gain (loss) arising from ineffective portion of commodity contracts	(325)	198	97
Total impact on purchased gas cost	(42,041)	8,563	(10,681)
Net loss on settled Treasury lock agreements reclassified from AOCI into interest expense	(853)	(4,230)	(3,489)
Total Impact from Cash Flow Hedges	(42,894)	4,333	(14,170)
Regulated Distribution Segment [Member]
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	0	0	0
Gain (loss) arising from ineffective portion of commodity contracts	0	0	0
Total impact on purchased gas cost	0	0	0
Net loss on settled Treasury lock agreements reclassified from AOCI into interest expense	(853)	(4,230)	(3,489)
Total Impact from Cash Flow Hedges	(853)	(4,230)	(3,489)
Nonregulated Segment [Member]
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	(41,716)	8,365	(10,778)
Gain (loss) arising from ineffective portion of commodity contracts	(325)	198	97
Total impact on purchased gas cost	(42,041)	8,563	(10,681)
Net loss on settled Treasury lock agreements reclassified from AOCI into interest expense	0	0	0
Total Impact from Cash Flow Hedges	$ (42,041)	$ 8,563	$ (10,681)