Fair Value Measurements (Fair Value Measurements Using Unobservable Inputs (Level 3)) (Details) (Derivative Financial Instruments [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2013		Mar. 31, 2012
Derivative Financial Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ (14,089)	[1]	$ (54,773)	[1]	$ (19,664)	[1]	$ (5,410)	[1]
Total Gains/Losses, Realized and Included in Earnings	4,539	[1],[2]	13,523	[1],[3]	6,801	[1],[4]	26,135	[1],[5]
Total Gains/Losses Unrealized and Included in Other Comprehensive Income (Loss)	(7,056)	[1]	(27,504)	[1]	(3,743)	[1]	(89,479)	[1]
Transfer In/Out of Level 3	0	[1]	0	[1]	0	[1]	0	[1]
Ending Balance	$ (16,606)	[1]	$ (68,754)	[1]	$ (16,606)	[1]	$ (68,754)	[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 three months ended March 31, 2013.

[3] Amounts are reported in Operating Revenues in the Consolidated Statement of Income for the three months ended March 31, 2012.

[4] Amounts are reported in Operating Revenues in the Consolidated Statement of Income for the six months ended March 31, 2013.

[5] Amounts are reported in Operating Revenues in the Consolidated Statement of Income for the six months ended March 31, 2012.