Financial Instruments Fair Value Hedges and Cash Flow Hedges (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Effect of Fair Value Hedges on Results of Operations [Abstract]
Commodity contracts	$ (792)	$ 2,165	$ 30,266
Fair value adjustment for natural gas inventory designated as the hedged item	2,486	15,938	(5,797)
Total (increase) decrease in purchased gas cost	1,694	18,103	24,469
Fair Value Hedge Basis Ineffectiveness	(919)	(208)	1,170
Fair Value Hedge Timing Ineffectiveness	2,613	18,311	23,299
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	8,365	(10,778)	(62,678)
Gain (loss) arising from ineffective portion of commodity contracts	198	97	(1,369)
Total impact on purchased gas cost	8,563	(10,681)	(64,047)
Net loss on settled Treasury lock agreements reclassified from AOCI into interest expense	(4,230)	(3,489)	(2,009)
Total Impact from Cash Flow Hedges	4,333	(14,170)	(66,056)
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	(4,230)	(3,489)	(2,009)
Total Impact from Cash Flow Hedges	(4,230)	(3,489)	(2,009)
Nonregulated Segment [Member]
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	8,365	(10,778)	(62,678)
Gain (loss) arising from ineffective portion of commodity contracts	198	97	(1,369)
Total impact on purchased gas cost	8,563	(10,681)	(64,047)
Net loss on settled Treasury lock agreements reclassified from AOCI into interest expense	0	0	0
Total Impact from Cash Flow Hedges	$ 8,563	$ (10,681)	$ (64,047)