CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 139,095,000	$ 157,894,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization, accretion and other, net	26,334,000	20,606,000
Stock-based compensation expense	5,019,000	4,061,000
Provision (release) for credit losses	15,250,000	250,000
Loss (gain) on sale of investment securities	(15,028,000)	9,000
Net realized (gain) loss on sales of premises, equipment, and real estate owned	(33,044,000)	(9,098,000)
Impairment loss on premises and equipment	6,431,000	0
Prepayment penalty from repayment of borrowings	13,809,000	0
Decrease (increase) in accrued interest receivable	(1,135,000)	(709,000)
Decrease (increase) in federal and state income tax receivable	0	1,804,000
Decrease (increase) in cash surrender value of bank owned life insurance	(4,253,000)	(4,356,000)
Decrease (increase) in other assets	(149,007,000)	(23,046,000)
Increase (decrease) in federal and state income tax liabilities	2,773,000	1,232,000
Increase (decrease) in accrued expenses and other liabilities	105,420,000	20,055,000
Net cash provided by (used in) operating activities	111,664,000	168,702,000
CASH FLOWS FROM INVESTING ACTIVITIES
Origination of loans and principal repayments, net	(832,183,000)	(496,438,000)
Loans purchased	(15,456,000)	0
FHLB & FRB stock purchased	(323,200,000)	(440,600,000)
FHLB & FRB stock redeemed	301,200,000	433,600,000
Available-for-sale securities purchased	(684,292,000)	(327,670,000)
Principal payments and maturities of available-for-sale securities	301,319,000	164,295,000
Proceeds from sales of available-for-sale securities	204,351,000	491,000
Principal payments and maturities of held-to-maturity securities	237,895,000	114,678,000
Proceeds from sales of real estate owned	2,339,000	8,484,000
Cash paid for acquisitions	(2,810,000)	0
Proceeds from sales of premises and equipment	55,213,000	11,669,000
Premises and equipment purchased and REO improvements	(22,641,000)	(30,845,000)
Net cash provided by (used in) investing activities	(778,265,000)	(562,336,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase (decrease) in customer accounts	1,118,830,000	413,252,000
Proceeds from borrowings	8,080,000,000	11,015,000,000
Repayments of borrowings	(7,543,809,000)	(10,840,000,000)
Proceeds from stock-based awards	141,000	712,000
Dividends paid on common stock	(49,935,000)	(46,749,000)
Treasury stock purchased	(112,129,000)	(103,935,000)
Increase (decrease) in borrower advances related to taxes and insurance, net	(27,415,000)	(23,468,000)
Net cash provided by (used in) financing activities	1,465,683,000	414,812,000
Increase (decrease) in cash and cash equivalents	799,082,000	21,178,000
Cash, cash equivalents and restricted cash at beginning of period	419,158,000	268,650,000
Cash, cash equivalents and restricted cash at end of period	1,218,240,000	289,828,000
Non-cash investing activities
Real estate acquired through foreclosure	1,329,000	1,669,000
Other personal property acquired through foreclosure	359,000	0
Non-cash financing activities
Stock issued upon exercise of warrants	0	1,082,000
Cash paid during the period for
Interest	119,022,000	143,740,000
Income taxes	$ 23,863,000	$ 25,655,000