Fair Value Measurements (Recurring Fair Value Measures Of Assets And Liabilities) (Details) (USD $)	Mar. 31, 2012	Sep. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents - Money Market Mutual Funds	$ 162,382,000	$ 32,444,000
Hedging Collateral Deposits	18,872,000	19,701,000
Total Assets	332,896,000	152,816,000
Total Liabilities	66,887,000	9,674,000
Total Net Assets/(Liabilities)	266,009,000	143,142,000
Commodity Futures Contracts - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	576,000
Derivative Financial Instruments	6,690,000	3,292,000
Over The Counter Swaps - Oil [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments		972,000
Derivative Financial Instruments	68,754,000	6,382,000
Over The Counter Swaps - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	121,184,000	75,113,000
Derivative Financial Instruments	(8,557,000)
Balanced Equity Mutual Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	24,234,000	19,882,000
Common Stock - Financial Services Industry [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	5,355,000	4,478,000
Other Common Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	293,000	226,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents - Money Market Mutual Funds	162,382,000	32,444,000
Hedging Collateral Deposits	18,872,000	19,701,000
Total Assets	211,712,000	76,731,000
Total Liabilities	6,690,000	3,292,000
Total Net Assets/(Liabilities)	205,022,000	73,439,000
Fair Value, Inputs, Level 1 [Member] | Commodity Futures Contracts - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	576,000
Derivative Financial Instruments	6,690,000	3,292,000
Fair Value, Inputs, Level 1 [Member] | Over The Counter Swaps - Oil [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments		0
Derivative Financial Instruments	0	0
Fair Value, Inputs, Level 1 [Member] | Over The Counter Swaps - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	0	0
Derivative Financial Instruments	0
Fair Value, Inputs, Level 1 [Member] | Balanced Equity Mutual Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	24,234,000	19,882,000
Fair Value, Inputs, Level 1 [Member] | Common Stock - Financial Services Industry [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	5,355,000	4,478,000
Fair Value, Inputs, Level 1 [Member] | Other Common Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	293,000	226,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents - Money Market Mutual Funds	0	0
Hedging Collateral Deposits	0	0
Total Assets	121,184,000	75,113,000
Total Liabilities	(8,557,000)	0
Total Net Assets/(Liabilities)	129,741,000	75,113,000
Fair Value, Inputs, Level 2 [Member] | Commodity Futures Contracts - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	0
Derivative Financial Instruments	0	0
Fair Value, Inputs, Level 2 [Member] | Over The Counter Swaps - Oil [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments		0
Derivative Financial Instruments	0	0
Fair Value, Inputs, Level 2 [Member] | Over The Counter Swaps - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	121,184,000	75,113,000
Derivative Financial Instruments	(8,557,000)
Fair Value, Inputs, Level 2 [Member] | Balanced Equity Mutual Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	0	0
Fair Value, Inputs, Level 2 [Member] | Common Stock - Financial Services Industry [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	0	0
Fair Value, Inputs, Level 2 [Member] | Other Common Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents - Money Market Mutual Funds	0	0
Hedging Collateral Deposits	0	0
Total Assets	0	972,000
Total Liabilities	68,754,000	6,382,000
Total Net Assets/(Liabilities)	(68,754,000)	(5,410,000)
Fair Value, Inputs, Level 3 [Member] | Commodity Futures Contracts - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	0
Derivative Financial Instruments	0	0
Fair Value, Inputs, Level 3 [Member] | Over The Counter Swaps - Oil [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments		972,000
Derivative Financial Instruments	68,754,000	6,382,000
Fair Value, Inputs, Level 3 [Member] | Over The Counter Swaps - Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments	0	0
Derivative Financial Instruments	0
Fair Value, Inputs, Level 3 [Member] | Balanced Equity Mutual Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	0	0
Fair Value, Inputs, Level 3 [Member] | Common Stock - Financial Services Industry [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	0	0
Fair Value, Inputs, Level 3 [Member] | Other Common Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Investments	$ 0	$ 0