Financial Instruments Fair Value Hedges and Cash Flow Hedges (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Effect of Fair Value Hedges on Results of Operations [Abstract]
Commodity contracts	$ 8,561	$ (7,314)
Fair value adjustment for natural gas inventory designated as the hedged item	(13,779)	(8,818)
Total (increase) decrease to purchased gas cost	5,218	16,132
Basis ineffectiveness	(620)	(241)
Timing ineffectiveness	5,838	16,373
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	(2,609)	(5,160)
Gain (loss) arising from ineffective portion of commodity contracts	(119)	(19)
Total impact on purchased gas cost	(2,728)	(5,179)
Loss on settled Treasury Lock agreements reclassified from AOCI into interest expense	(1,058)	(502)
Total Impact from Cash Flow Hedges	(3,786)	(5,681)
Natural Gas 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
Gain (loss) arising from ineffective portion of commodity contracts	0	0
Total impact on purchased gas cost	0	0
Loss on settled Treasury Lock agreements reclassified from AOCI into interest expense	(1,058)	(502)
Total Impact from Cash Flow Hedges	(1,058)	(502)
Nonregulated Segment [Member]
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	(2,609)	(5,160)
Gain (loss) arising from ineffective portion of commodity contracts	(119)	(19)
Total impact on purchased gas cost	(2,728)	(5,179)
Loss on settled Treasury Lock agreements reclassified from AOCI into interest expense	0	0
Total Impact from Cash Flow Hedges	$ (2,728)	$ (5,179)