CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 71,193	$ 70,808	$ 564,317	$ 360,568
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax of $92, $490, $(246) and $893	310	851	(736)	1,553
Cash flow hedges:
Amortization and unrealized gain (loss) on interest rate agreements, net of tax of $2,460, $(10,667), $8,486 and $44,194	8,320	(18,556)	29,609	76,888
Net unrealized gains on commodity cash flow hedges, net of tax of $0, $0, $0 and $3,183	0	0	0	4,982
Total other comprehensive income (loss)	8,630	(17,705)	28,873	83,423
Total comprehensive income	$ 79,823	$ 53,103	$ 593,190	$ 443,991