Accumulated Other Comprehensive Income Components (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ 38,878	$ (47,607)
Other comprehensive income before reclassifications	(48,060)	79,068
Amounts reclassified from accumulated other comprehensive income	(3,211)	7,417
Net current-period other comprehensive income (loss)	(51,271)	86,485	853
Accumulated other comprehensive income (loss), ending balance	(12,393)	38,878	(47,607)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	5,448	5,661
Other comprehensive income before reclassifications	3,009	1,162
Amounts reclassified from accumulated other comprehensive income	(795)	(1,375)
Net current-period other comprehensive income (loss)	2,214	(213)
Accumulated other comprehensive income (loss), ending balance	7,662	5,448
Accumulated Net Gain (Loss) from Interest Rate Hedges [Member] [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	37,906	(44,273)
Other comprehensive income before reclassifications	(58,973)	79,963
Amounts reclassified from accumulated other comprehensive income	2,686	2,216
Net current-period other comprehensive income (loss)	(56,287)	82,179
Accumulated other comprehensive income (loss), ending balance	(18,381)	37,906
Accumulated Net Gain (Loss) from Commodity Contracts Cash Flow Hedges [Member] [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(4,476)	(8,995)
Other comprehensive income before reclassifications	7,904	(2,057)
Amounts reclassified from accumulated other comprehensive income	(5,102)	6,576
Net current-period other comprehensive income (loss)	2,802	4,519
Accumulated other comprehensive income (loss), ending balance	$ (1,674)	$ (4,476)