Fair Value Measurements (Details) (USD $)	Mar. 31, 2013	Sep. 30, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	$ 48,137,000	$ 27,138,000
Hedged portion of gas stored underground	89,342,000	67,192,000
Total available for sale securities	66,470,000	64,398,000
Total assets	203,949,000	158,728,000
Total liabilities	59,000	94,846,000
Fair Value [Abstract]
Cash Collateral Right To Reclaim Cash	12,000,000	23,700,000
Cash Held In Margin Accounts Offset Current Risk Management Liabilities	8,300,000	5,900,000
Cash Held In Margin Accounts Classified Current Risk Management Asset	3,700,000	17,800,000
Debt Instrument Carrying Amount	2,460,000,000	1,960,131,000
Debt Instrument Fair Value	2,876,673,000
Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	11,761,000	1,634,000
Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	31,092,000	40,212,000
Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available for sale securities	23,617,000	22,552,000
Natural Gas Distribution Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	40,185,000	9,365,000
Total liabilities	59,000	85,625,000
Nonregulated Segment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial instruments	7,952,000	17,773,000
Total liabilities	0	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	489,000	714,000
Hedged portion of gas stored underground	89,342,000	67,192,000
Total available for sale securities	31,092,000	40,212,000
Total assets	120,923,000	108,118,000
Total liabilities	969,000	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	31,092,000	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	489,000	714,000
Total liabilities	969,000	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	179,620,000	189,200,000
Hedged portion of gas stored underground	0	0
Total available for sale securities	35,378,000	24,186,000
Total assets	214,998,000	213,386,000
Total liabilities	143,033,000	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	11,761,000	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	23,617,000	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	40,185,000	9,365,000
Total liabilities	59,000	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	139,435,000	179,835,000
Total liabilities	142,974,000	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	(131,972,000)	(162,776,000)
Hedged portion of gas stored underground	0	0
Total available for sale securities	0	0
Total assets	(131,972,000)	(162,776,000)
Total liabilities	(143,943,000)	(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	(131,972,000)	(162,776,000)
Total liabilities	$ (143,943,000)	$ (186,451,000)