CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 133,367	$ 116,425	$ 220,383	$ 196,890
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax	(252)	(200)	2,142	(573)
Amortization and unrealized gains (losses) on interest rate agreements, net of tax	(27,047)	23,509	(13,105)	35,773
Net unrealized gains (losses) on commodity cash flow hedges, net of tax	1,101	8,838	8,919	8,473
Total other comprehensive income (loss)	(26,198)	32,147	(2,044)	43,673
Total comprehensive income (loss)	$ 107,169	$ 148,572	$ 218,339	$ 240,563