Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 257,426,000	$ 236,330,000	$ 183,615,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization, accretion and other, net	22,970,000	64,050,000	33,914,000
Stock-based compensation expense	7,914,000	6,808,000	6,381,000
Provision (release) for credit losses	41,500,000	3,000,000	500,000
Loss (gain) on sale of investment securities	(33,000)	(99,000)	(14,000)
Prepayment penalty on early extinguishment of debt	0	0	13,788,000
Gain on early termination of long term borrowing hedge	0	0	(14,110,000)
Gain on settlements of bank owned life insurance	(821,000)	(1,385,000)	0
Impairment loss on premises and equipment	6,000	0	944,000
Net realized (gain) loss on sales of premises, equipment and real estate owned	(1,153,000)	655,000	(593,000)
Decrease (increase) in accrued interest receivable	(23,131,000)	(13,236,000)	3,163,000
Decrease (increase) in federal and state income tax receivable	(6,650,000)	3,877,000	1,831,000
Decrease (increase) in cash surrender value of bank owned life insurance	(5,976,000)	(5,549,000)	(5,514,000)
Decrease (increase) in other assets	(67,342,000)	(100,146,000)	155,599,000
Increase (decrease) in federal and state income tax liabilities	(3,306,000)	8,386,000	(15,781,000)
Increase (decrease) in accrued expenses and other liabilities	(7,447,000)	65,774,000	(49,269,000)
Net cash provided (used) by operating activities	213,957,000	268,465,000	314,454,000
CASH FLOWS FROM INVESTING ACTIVITIES
Origination of loans and principal repayments, net	(1,330,399,000)	(1,748,955,000)	(556,274,000)
Loans purchased	(79,965,000)	(576,697,000)	(488,147,000)
FHLB & FRB stock purchase	(654,805,000)	(293,800,000)	(296,073,000)
FHLB & FRB stock redeemed	623,058,000	301,590,000	335,200,000
Available-for-sale securities purchased	(376,481,000)	(587,942,000)	(530,227,000)
Principal payments and maturities of available-for-sale securities	420,154,000	510,156,000	646,532,000
Proceeds from sales of available-for-sale investment securities	1,169,000	5,020,000	1,499,000
Held-to-maturity securities purchased	0	(195,357,000)	0
Principal payments and maturities of held-to-maturity securities	39,414,000	95,326,000	332,001,000
Proceeds from sales of real estate owned	7,192,000	6,978,000	3,340,000
Proceeds from settlements of bank owned life insurance	1,809,000	2,266,000	0
Purchase of strategic investments	(12,500,000)	0	0
Net cash received (paid) in business combinations	(2,590,000)	0	(1,500,000)
Proceeds from sales of premises and equipment	1,090,000	41,000	3,376,000
Premises and equipment purchased and REO improvements	(15,063,000)	(11,790,000)	(29,472,000)
Net cash provided (used) by investing activities	(1,377,917,000)	(2,493,164,000)	(579,745,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase (decrease) in customer accounts	40,759,000	487,458,000	1,762,488,000
Proceeds from borrowings	17,175,000,000	7,345,000,000	7,400,000,000
Repayments of borrowings	(15,650,000,000)	(6,940,000,000)	(8,393,788,000)
Proceeds from the early termination of long term borrowing hedge	0	0	14,110,000
Proceeds from stock-based awards	1,089,000	1,823,000	339,000
Proceeds from issuance of preferred stock, net	0	0	293,325,000
Dividends paid on common stock	(63,792,000)	(61,576,000)	(65,876,000)
Dividends paid on preferred stock	(14,625,000)	(14,625,000)	(6,378,000)
Proceeds from employee stock purchase	177,000	0	0
Treasury stock purchased	(30,463,000)	(3,260,000)	(348,651,000)
Increase (decrease) in advance payments by borrowers for taxes and insurance	2,499,000	3,035,000	(2,446,000)
Net cash provided (used) by financing activities	1,460,644,000	817,855,000	653,123,000
Increase (decrease) in cash and cash equivalents	296,684,000	(1,406,844,000)	387,832,000
Cash and cash equivalents at beginning of year	683,965,000	2,090,809,000	1,702,977,000
Cash and cash equivalents at end of year	980,649,000	683,965,000	2,090,809,000
Non-cash investing activities
Real estate acquired through foreclosure	121,000	73,000	221,000
Other personal property acquired through foreclosure	0	577,000	0
Non-cash financing activities
Preferred stock dividend payable	3,656,000	3,656,000	3,656,000
Cash paid during the year for
Interest	364,386,000	65,175,000	71,845,000
Income taxes	$ 61,245,000	$ 35,098,000	$ 47,854,000