CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 47,422	$ 34,852	$ 131,244	$ 139,095
Other comprehensive income (loss) net of tax:
Net unrealized gain (loss) during the period on available-for-sale investment securities, net of tax	2,027	12,294	7,289	22,186
Reclassification adjustment of net (gain) loss from sale of available-for-sale securities included in net income, net of tax	0	0	0	(11,572)
Net unrealized gain (loss) from investment securities, net of reclassification adjustment	2,027	12,294	7,289	10,614
Net unrealized gain (loss) during the period on borrowings cash flow hedges, net of tax	(18,083)	(6,195)	51,743	(13,346)
Reclassification adjustment of net (gain) loss included in net income during the period from hedging derivatives, net of tax	0	0	(10,865)	0
Net unrealized gain (loss) in cash flow hedging instruments, net of reclassification adjustment	(18,083)	(6,195)	40,878	(13,346)
Other comprehensive income (loss)	(16,056)	6,099	48,167	(2,732)
Comprehensive income	$ 31,366	$ 40,951	$ 179,411	$ 136,363