CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 41,246,000	$ 35,098,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization, and accretion, net	12,087,000	2,054,000
Cash received from (paid to) FDIC under loss share	0	1,975,000
Stock based compensation	2,745,000	1,180,000
Loss (gain) on sale of investment securities	(968,000)	0
Decrease (increase) in accrued interest receivable	(449,000)	2,170,000
Decrease (increase) in federal and state income tax receivable	16,047,000	16,577,000
Decrease (increase) in cash surrender value of bank owned life insurance	(1,739,000)	(785,000)
Gain on settlement of bank owned life insurance	(649,000)	0
Net realized (gain) loss on sales of premises, equipment, and real estate owned	657,000	(2,310,000)
Decrease (increase) in other assets	14,153,000	(3,754,000)
Increase (decrease) in accrued expenses and other liabilities	(41,265,000)	15,870,000
Net cash provided by (used in) operating activities	41,865,000	68,075,000
CASH FLOWS FROM INVESTING ACTIVITIES
Origination of loans and principal repayments, net	(227,028,000)	(179,768,000)
Loans purchased	0	(51,646,000)
FHLB & FRB stock purchased	(9,000)	(6,809,000)
FHLB & FRB stock redemption	24,000	2,901,000
Available-for-sale securities purchased	0	(50,741,000)
Principal payments and maturities of available-for-sale securities	112,469,000	114,764,000
Proceeds on available-for-sale securities sold	350,890,000	0
Held-to-maturity securities purchased	(415,729,000)	0
Principal payments and maturities of held-to-maturity securities	78,778,000	43,569,000
Proceeds from sales of real estate owned	6,457,000	26,664,000
Proceeds from settlement of bank owned life insurance	1,231,000	0
Purchase of bank owned life insurance	0	0
Decrease (increase) in intangible assets	0	0
Proceeds from sales of premises and equipment	1,722,000	0
Premises and equipment purchased and REO improvements	(1,252,000)	(17,183,000)
Net cash provided by (used in) investing activities	(92,447,000)	(118,249,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase (decrease) in customer accounts	46,799,000	19,492,000
Proceeds from borrowings	0	204,000,000
Repayments of borrowings	0	(106,000,000)
Proceeds from exercise of common stock options	4,362,000	5,042,000
Dividends paid on common stock	(12,422,000)	(12,036,000)
Treasury stock purchased	(20,385,000)	(9,938,000)
Increase (decrease) in advance payments by borrowers for taxes and insurance	(19,302,000)	(28,476,000)
Net cash provided by (used in) financing activities	(948,000)	72,084,000
Increase (decrease) in cash and cash equivalents	(51,530,000)	21,910,000
Cash and cash equivalents at beginning of period	450,368,000	284,049,000
Cash and cash equivalents at end of period	398,838,000	305,959,000
Non-cash investing and financing activities
Real estate acquired through foreclosure	1,589,000	5,308,000
Stock issued upon exercise of warrants	1,523,000	0
Cash paid during the period for
Interest	28,737,000	29,195,000
Income taxes	$ 0	$ 8,000