Financial Instruments Fair Value Hedges and Cash Flow Hedges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Effect of Fair Value Hedges on Results of Operations [Abstract]
Commodity contracts	$ (1,715)	$ 1,991	$ 5,754	$ (2,983)
Fair value adjustment for natural gas inventory designated as the hedged item	5,350	(2,258)	(6,291)	4,071
Total (increase) decrease to purchased gas cost	3,635	(267)	(537)	1,088
Basis ineffectiveness	599	817	908	(382)
Timing ineffectiveness	3,036	(1,084)	(1,445)	1,470
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	(16,488)	4,209	(29,222)	8,783
Gain (loss) arising from ineffective portion of commodity contracts	11	179	(316)	203
Total impact on purchased gas cost	(16,477)	4,388	(29,538)	8,986
Loss on settled Treasury Lock agreements reclassified from AOCI into interest expense	(137)	(1,057)	(717)	(3,172)
Total Impact from Cash Flow Hedges	(16,614)	3,331	(30,255)	5,814
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	0
Gain (loss) arising from ineffective portion of commodity contracts	0	0	0	0
Total impact on purchased gas cost	0	0	0	0
Loss on settled Treasury Lock agreements reclassified from AOCI into interest expense	(137)	(1,057)	(717)	(3,172)
Total Impact from Cash Flow Hedges	(137)	(1,057)	(717)	(3,172)
Nonregulated Segment [Member]
Cash Flow Hedge [Line Items]
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts	(16,488)	4,209	(29,222)	8,783
Gain (loss) arising from ineffective portion of commodity contracts	11	179	(316)	203
Total impact on purchased gas cost	(16,477)	4,388	(29,538)	8,986
Loss on settled Treasury Lock agreements reclassified from AOCI into interest expense	0	0	0	0
Total Impact from Cash Flow Hedges	$ (16,477)	$ 4,388	$ (29,538)	$ 8,986