Accumulated Other Comprehensive Income Components (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ 38,878	$ (47,607)
Other comprehensive income (loss) before reclassifications	(370)	38,188
Amounts reclassified from accumulated other comprehensive income	(1,674)	5,485
Net current-period other comprehensive income (loss)	(2,044)	43,673
Accumulated other comprehensive income (loss), ending balance	36,834	(3,934)
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 (loss) before reclassifications	2,369	1,135
Amounts reclassified from accumulated other comprehensive income	(227)	(1,708)
Net current-period other comprehensive income (loss)	2,142	(573)
Accumulated other comprehensive income (loss), ending balance	7,590	5,088
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 (loss) before reclassifications	(14,448)	34,900
Amounts reclassified from accumulated other comprehensive income	1,343	873
Net current-period other comprehensive income (loss)	(13,105)	35,773
Accumulated other comprehensive income (loss), ending balance	24,801	(8,500)
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 (loss) before reclassifications	11,709	2,153
Amounts reclassified from accumulated other comprehensive income	(2,790)	6,320
Net current-period other comprehensive income (loss)	8,919	8,473
Accumulated other comprehensive income (loss), ending balance	$ 4,443	$ (522)