Fair Value Measurements (Fair Value Measurements Using Unobservable Inputs (Level 3)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Gains/Losses, Realized and Included in Earnings	$ 0		$ 0
Derivative Financial Instruments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, Beginning of Year	(5,410)	[1]	(16,483)	[1]
Total Gains/Losses, Realized and Included in Earnings	46,174	[1],[2]	41,354	[1],[3]
Total Gains/Losses, Unrealized and Included in Other Comprehensive Income (Loss)	(60,428)	[1]	(30,281)	[1]
Transfer In/Out of Level 3	0	[1]	0	[1]
Balance, End of Year	$ (19,664)	[1]	$ (5,410)	[1]

[1] Derivative Financial Instruments are shown on a net basis.

[2] Amounts are reported in Operating Revenues in the Consolidated Statement of Income for the year ended September 30, 2012.

[3] Amounts are reported in Operating Revenues in the Consolidated Statement of Income for the year ended September 30, 2011.