CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 44,112	$ 43,004	$ 127,428	$ 119,825
Other comprehensive income (loss) net of tax:
Net unrealized gain (loss) on available-for-sale investment securities	3,171	(965)	(8,224)	(4,409)
Reclassification adjustment of net gain (loss) from sale of available-for-sale securities included in net income	0	0	968	0
Related tax benefit (expense)	(1,165)	355	2,667	1,620
Other comprehensive income (loss) for available for sale securities, net of tax	2,006	(610)	(4,589)	(2,789)
Net unrealized gain (loss) on long-term borrowing hedge	(2,856)	(10,290)	28,810	(20,978)
Related tax benefit (expense)	1,049	3,782	(10,587)	7,709
Other comprehensive income (loss) on long term borrowing hedge, net of tax	(1,807)	(6,508)	18,223	(13,269)
Other comprehensive income (loss) net of tax	199	(7,118)	13,634	(16,058)
Comprehensive income	$ 44,311	$ 35,886	$ 141,062	$ 103,767