Accumulated Other Comprehensive Income Components (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ (12,393)	$ 38,878
Other comprehensive income (loss) before reclassifications	(67,803)	(23,542)
Amounts reclassified from accumulated other comprehensive income	17,955	(4,036)
Net current-period other comprehensive income (loss)	(49,848)	(27,578)
Accumulated other comprehensive income (loss), ending balance	(62,241)	11,300
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	7,662	5,448
Other comprehensive income (loss) before reclassifications	30	3,212
Amounts reclassified from accumulated other comprehensive income	(326)	(693)
Net current-period other comprehensive income (loss)	(296)	2,519
Accumulated other comprehensive income (loss), ending balance	7,366	7,967
Accumulated Net Gain (Loss) from Interest Rate Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(18,381)	37,906
Other comprehensive income (loss) before reclassifications	(30,436)	(38,559)
Amounts reclassified from accumulated other comprehensive income	455	2,014
Net current-period other comprehensive income (loss)	(29,981)	(36,545)
Accumulated other comprehensive income (loss), ending balance	(48,362)	1,361
Accumulated Net Gain (Loss) from Commodity Contracts Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(1,674)	(4,476)
Other comprehensive income (loss) before reclassifications	(37,397)	11,805
Amounts reclassified from accumulated other comprehensive income	17,826	(5,357)
Net current-period other comprehensive income (loss)	(19,571)	6,448
Accumulated other comprehensive income (loss), ending balance	$ (21,245)	$ 1,972