CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 137,684	$ 133,367	$ 235,279	$ 220,383
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax	962	(252)	(105)	2,142
Amortization and unrealized gains (losses) on interest rate agreements, net of tax	(32,669)	(27,047)	(84,456)	(13,105)
Net unrealized gains (losses) on commodity cash flow hedges, net of tax	(2,182)	1,101	(31,134)	8,919
Total other comprehensive income (loss)	(33,889)	(26,198)	(115,695)	(2,044)
Total comprehensive income (loss)	$ 103,795	$ 107,169	$ 119,584	$ 218,339