CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 152,335,000	$ 127,428,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization, and accretion expense, net	38,980,000	29,602,000
Cash received from (paid to) FDIC under loss share agreements, net	1,595,000	813,000
Stock based compensation expense	3,634,000	5,126,000
Provision (release) for loan losses	50,000	(1,600,000)
Loss (gain) on sale of investment securities	0	(968,000)
Decrease (increase) in accrued interest receivable	(2,027,000)	(1,257,000)
Decrease (increase) in federal and state income tax receivable	(4,293,000)	16,047,000
Decrease (increase) in cash surrender value of bank owned life insurance	(4,490,000)	(4,907,000)
Gain on bank owned life insurance	(2,416,000)	(4,983,000)
Net realized (gain) loss on sales of premises, equipment, and real estate owned	(1,333,000)	(1,691,000)
Decrease (increase) in other assets	(878,000)	6,618,000
Increase (decrease) in accrued expenses and other liabilities	(40,862,000)	(47,859,000)
Net cash provided by (used in) operating activities	140,295,000	122,369,000
CASH FLOWS FROM INVESTING ACTIVITIES
Origination of loans and principal repayments, net	(308,167,000)	(668,413,000)
Loans purchased	(143,605,000)	(72,856,000)
FHLB & FRB stock purchased	(408,800,000)	(93,009,000)
FHLB & FRB stock redeemed	403,000,000	85,224,000
Available-for-sale securities purchased	(166,696,000)	0
Principal payments and maturities of available-for-sale securities	156,240,000	290,243,000
Proceeds from sales of available-for-sale securities	0	350,890,000
Held-to-maturity securities purchased	(170,836,000)	(415,729,000)
Principal payments and maturities of held-to-maturity securities	143,837,000	176,333,000
Proceeds from sales of real estate owned	11,960,000	13,780,000
Proceeds from settlement of bank owned life insurance	3,484,000	6,913,000
Cash paid for acquisitions	(2,211,000)	0
Proceeds from sales of premises and equipment	1,000	3,956,000
Premises and equipment purchased and REO improvements	(22,604,000)	(9,541,000)
Net cash provided by (used in) investing activities	(504,397,000)	(332,209,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase (decrease) in customer accounts	452,694,000	33,654,000
Proceeds from borrowings	10,220,000,000	2,325,000,000
Repayments of borrowings	(10,075,000,000)	(2,130,000,000)
Proceeds from exercise of common stock options and related tax benefit	1,288,000	7,078,000
Dividends paid on common stock	(41,091,000)	(61,341,000)
Treasury stock purchased	(136,941,000)	(46,470,000)
Increase (decrease) in borrower advances related to taxes and insurance, net	(23,999,000)	(9,197,000)
Net cash provided by (used in) financing activities	396,951,000	118,724,000
Increase (decrease) in cash and cash equivalents	32,849,000	(91,116,000)
Cash and cash equivalents at beginning of period	313,070,000	450,368,000
Cash and cash equivalents at end of period	345,919,000	359,252,000
Non-cash investing activities
Real estate acquired through foreclosure	1,517,000	2,323,000
Non-cash financing activities
Stock issued upon exercise of warrants	3,836,000	7,546,000
Cash paid during the period for
Interest	95,394,000	82,919,000
Income taxes	$ 34,160,000	$ 33,228,000