CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 289,817	$ 243,194	$ 216,717
Other comprehensive income (loss), net of tax [Abstract]
Net unrealized holding gains (losses) on available-for-sale securities, net of tax of $1,199, $(186) and $1,881	2,214	(213)	3,103
Amortization and unrealized gain (loss) on interest rate agreements, net of tax of $(32,353), $47,236 and $(5,388)	(56,287)	82,179	(10,116)
Net unrealized gains on commodity cash flow hedges, net of tax of $1,791, $2,889 and $5,029	2,802	4,519	7,866
Total other comprehensive income (loss)	(51,271)	86,485	853
Total comprehensive income	$ 238,546	$ 329,679	$ 217,570