Fair Value Measurements (Details) (USD $)	Jun. 30, 2013	Sep. 30, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	$ 99,478,000	$ 27,138,000
Hedged portion of gas stored underground	76,706,000	67,192,000
Total available for sale securities	71,646,000	64,398,000
Total assets	247,830,000	158,728,000
Total liabilities	3,161,000	94,846,000
Fair Value [Abstract]
Cash Collateral Right To Reclaim Cash	14,300,000	23,700,000
Cash Held In Margin Accounts Offset Current Risk Management Liabilities	2,500,000	5,900,000
Cash Held In Margin Accounts Classified Current Risk Management Asset	11,800,000	17,800,000
Debt Instrument Carrying Amount	2,460,000,000	1,960,131,000
Debt Instrument Fair Value	2,707,340,000
Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	5,122,000	1,634,000
Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	39,051,000	40,212,000
Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	27,473,000	22,552,000
Natural Gas Distribution Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	87,482,000	9,365,000
Total liabilities	1,094,000	85,625,000
Nonregulated Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	11,996,000	17,773,000
Total liabilities	2,067,000	9,221,000
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	1,196,000	714,000
Hedged portion of gas stored underground	76,706,000	67,192,000
Total available for sale securities	39,051,000	40,212,000
Total assets	116,953,000	108,118,000
Total liabilities	179,000	4,563,000
Fair Value Inputs Level 1 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Fair Value Inputs Level 1 [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	39,051,000	40,212,000
Fair Value Inputs Level 1 [Member] | Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Fair Value Inputs Level 1 [Member] | Natural Gas Distribution Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	0	0
Total liabilities	0	0
Fair Value Inputs Level 1 [Member] | Nonregulated Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	1,196,000	714,000
Total liabilities	179,000	4,563,000
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	217,560,000	189,200,000
Hedged portion of gas stored underground	0	0
Total available for sale securities	32,595,000	24,186,000
Total assets	250,155,000	213,386,000
Total liabilities	136,512,000	276,734,000
Fair Value Inputs Level 2 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	5,122,000	1,634,000
Fair Value Inputs Level 2 [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Fair Value Inputs Level 2 [Member] | Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	27,473,000	22,552,000
Fair Value Inputs Level 2 [Member] | Natural Gas Distribution Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	87,482,000	9,365,000
Total liabilities	1,094,000	85,625,000
Fair Value Inputs Level 2 [Member] | Nonregulated Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	130,078,000	179,835,000
Total liabilities	135,418,000	191,109,000
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	0	0
Hedged portion of gas stored underground	0	0
Total available for sale securities	0	0
Total assets	0	0
Total liabilities	0	0
Fair Value Inputs Level 3 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Fair Value Inputs Level 3 [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Fair Value Inputs Level 3 [Member] | Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Fair Value Inputs Level 3 [Member] | Natural Gas Distribution Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	0	0
Total liabilities	0	0
Fair Value Inputs Level 3 [Member] | Nonregulated Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	0	0
Total liabilities	0	0
Netting And Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	(119,278,000)	(162,776,000)
Hedged portion of gas stored underground	0	0
Total available for sale securities	0	0
Total assets	(119,278,000)	(162,776,000)
Total liabilities	(133,530,000)	(186,451,000)
Netting And Collateral [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Netting And Collateral [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Netting And Collateral [Member] | Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	0	0
Netting And Collateral [Member] | Natural Gas Distribution Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	0	0
Total liabilities	0	0
Netting And Collateral [Member] | Nonregulated Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	(119,278,000)	(162,776,000)
Total liabilities	$ (133,530,000)	$ (186,451,000)