Financial Instruments Balance Sheet Location (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013
Derivatives Fair Value [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 9,000	$ 10,100
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	7,700	14,700
Natural Gas Distribution Segment [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	134,812	111,191
Derivative Asset, Contract Netting	0	0
Derivative Asset, Net of Contract Netting	134,812	111,191
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Asset	134,812	111,191
Derivative Liability, Fair Value, Gross Liability	(36)	(1,543)
Derivative Liability, Contract Netting	0	0
Derivative Liability, Net of Contract Netting	(36)	(1,543)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0	0
Derivative Liability	(36)	(1,543)
Nonregulated Segment [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	104,049	115,880
Derivative Asset, Contract Netting	(101,435)	(115,875)
Derivative Asset, Net of Contract Netting	2,614	5
Derivative, Collateral, Right to Reclaim Cash	9,001	10,124
Derivative Asset	11,615	10,129
Derivative Liability, Fair Value, Gross Liability	(109,142)	(130,580)
Derivative Liability, Contract Netting	101,435	115,875
Derivative Liability, Net of Contract Netting	(7,707)	(14,705)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	7,707	14,705
Derivative Liability	0	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	128,411	107,512
Derivative Liability, Fair Value, Gross Liability	0	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Other Current Assets [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	83,578
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Deferred Charges And Other Assets [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	44,833	107,512
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Deferred Charges And Other Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Other Current Liabilities [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Other Current Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Deferred Credits And Other Liabilities [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Designated As Hedging Instrument [Member] | Natural Gas Distribution Segment [Member] | Deferred Credits And Other Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	13,021	9,510
Derivative Liability, Fair Value, Gross Liability	(13,072)	(13,812)
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Other Current Assets [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	12,238	9,094
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Deferred Charges And Other Assets [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Deferred Charges And Other Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	783	416
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Other Current Liabilities [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Other Current Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(12,089)	(12,173)
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Deferred Credits And Other Liabilities [Member] | Interest Rate Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Designated As Hedging Instrument [Member] | Nonregulated Segment [Member] | Deferred Credits And Other Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(983)	(1,639)
Nondesignated [Member] | Natural Gas Distribution Segment [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	6,401	3,679
Derivative Liability, Fair Value, Gross Liability	(36)	(1,543)
Nondesignated [Member] | Natural Gas Distribution Segment [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,356	1,837
Nondesignated [Member] | Natural Gas Distribution Segment [Member] | Deferred Charges And Other Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,045	1,842
Nondesignated [Member] | Natural Gas Distribution Segment [Member] | Other Current Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(36)	(1,543)
Nondesignated [Member] | Natural Gas Distribution Segment [Member] | Deferred Credits And Other Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Nondesignated [Member] | Nonregulated Segment [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	91,028	106,370
Derivative Liability, Fair Value, Gross Liability	(96,070)	(116,768)
Nondesignated [Member] | Nonregulated Segment [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	55,288	65,388
Nondesignated [Member] | Nonregulated Segment [Member] | Deferred Charges And Other Assets [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	35,740	40,982
Nondesignated [Member] | Nonregulated Segment [Member] | Other Current Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(63,144)	(70,876)
Nondesignated [Member] | Nonregulated Segment [Member] | Deferred Credits And Other Liabilities [Member] | Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ (32,926)	$ (45,892)