Financial Instruments Balance Sheet Location (Details) (USD $)	Sep. 30, 2013		Sep. 30, 2012
Derivatives, Fair Value [Line Items]
Derivative Asset, Current	$ 18,099,000		$ 24,707,000
Derivative Asset, Noncurrent	109,354,000		2,283,000
Derivative Liability, Current	(1,543,000)		(85,381,000)
Derivative Liability, Noncurrent	(6,133,000)		(9,206,000)
Derivative Assets (Liabilities), at Fair Value, Net	119,777,000		(67,597,000)
Cash Collateral Right To Reclaim Cash	24,800,000		23,700,000
Cash Held In Margin Accounts Offset Current Risk Management Liabilities	8,600,000		5,900,000
Cash Held In Margin Accounts Classified Current Risk Management Asset	16,200,000		17,800,000
Disposal Group, Including Discontinued Operation, Derivative Assets, Current			100,000
Disposal Group, Including Discontinued Operation, Derivative Liabilities, Current			300,000
Derivative, Fair Value, Net	94,948,000		(91,383,000)
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	103,210,000		(92,602,000)
Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	9,094,000		19,301,000
Designated as Hedging Instrument [Member] | Deferred Charges And Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	107,928,000		1,923,000
Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(12,173,000)		(108,827,000)
Designated as Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(1,639,000)		(4,999,000)
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	(8,262,000)		1,219,000
Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	67,225,000		105,475,000
Not Designated as Hedging Instrument [Member] | Deferred Charges And Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	42,824,000		63,215,000
Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(72,419,000)		(100,409,000)
Not Designated as Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(45,892,000)		(67,062,000)
Natural Gas Distribution Segment [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Current	1,837,000		6,934,000	[1]
Derivative Asset, Noncurrent	109,354,000		2,283,000
Derivative Liability, Current	(1,543,000)		(85,366,000)	[1]
Derivative Liability, Noncurrent	0		0
Derivative Assets (Liabilities), at Fair Value, Net	109,648,000		(76,149,000)
Derivative, Fair Value, Net	109,648,000		(76,260,000)
Natural Gas Distribution Segment [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	107,512,000		(85,040,000)
Natural Gas Distribution Segment [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Natural Gas Distribution Segment [Member] | Designated as Hedging Instrument [Member] | Deferred Charges And Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	107,512,000		0
Natural Gas Distribution Segment [Member] | Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	0		(85,040,000)
Natural Gas Distribution Segment [Member] | Designated as Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	0		0
Natural Gas Distribution Segment [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	2,136,000		8,780,000
Natural Gas Distribution Segment [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,837,000		7,082,000	[2]
Natural Gas Distribution Segment [Member] | Not Designated as Hedging Instrument [Member] | Deferred Charges And Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,842,000		2,283,000
Natural Gas Distribution Segment [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(1,543,000)		(585,000)	[3]
Natural Gas Distribution Segment [Member] | Not Designated as Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	0		0
Nonregulated Segment [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Current	16,262,000	[4]	17,773,000	[5]
Derivative Asset, Noncurrent	0		0
Derivative Liability, Current	0	[4]	(15,000)	[5]
Derivative Liability, Noncurrent	(6,133,000)		(9,206,000)
Derivative Assets (Liabilities), at Fair Value, Net	10,129,000		8,552,000
Cash Collateral Right To Reclaim Cash	24,800,000		23,700,000
Cash Held In Margin Accounts Offset Current Risk Management Liabilities	8,600,000		5,900,000
Cash Held In Margin Accounts Classified Current Risk Management Asset	16,200,000		17,800,000
Derivative, Fair Value, Net	(14,700,000)		(15,123,000)
Nonregulated Segment [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	(4,302,000)		(7,562,000)
Nonregulated Segment [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	9,094,000		19,301,000
Nonregulated Segment [Member] | Designated as Hedging Instrument [Member] | Deferred Charges And Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	416,000		1,923,000
Nonregulated Segment [Member] | Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(12,173,000)		(23,787,000)
Nonregulated Segment [Member] | Designated as Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(1,639,000)		(4,999,000)
Nonregulated Segment [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	(10,398,000)		(7,561,000)
Nonregulated Segment [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	65,388,000		98,393,000
Nonregulated Segment [Member] | Not Designated as Hedging Instrument [Member] | Deferred Charges And Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	40,982,000		60,932,000
Nonregulated Segment [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	(70,876,000)		(99,824,000)
Nonregulated Segment [Member] | Not Designated as Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Liability	$ (45,892,000)		$ (67,062,000)

[1] The September 30, 2012 amounts are presented net of assets and liabilities held for sale in conjunction with the sale of our Georgia operations. At September 30, 2012, assets and liabilities held for sale included $0.1 million of current assets from risk management activities and $0.3 million of current liabilities from risk management activities.

[2] Other current assets not designated as hedges in our natural gas distribution segment include $0.1 million related to risk management assets that were classified as assets held for sale at September 30, 2012.

[3] Other current liabilities not designated as hedges in our natural gas distribution segment include $0.3 million related to risk management liabilities that were classified as assets held for sale at September 30, 2012.

[4] Includes $24.8 million of cash held on deposit to collateralize certain financial instruments. Of this amount, $8.6 million was used to offset current risk management liabilities under master netting arrangements and the remaining $16.2 million is classified as current risk management assets.

[5] Includes $23.7 million of cash held on deposit to collateralize certain financial instruments. Of this amount, $5.9 million was used to offset current risk management liabilities under master netting arrangements and the remaining $17.8 million is classified as current risk management assets.