Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 64,540	$ 94,243	$ 98,927
Adjustments to reconcile net income to net cash provided by operating activities:
FHLB stock dividends	(5,827)	(7,823)	(10,962)
Provision for credit losses	22,300	750	0
Originations of loans receivable held-for-sale ("LHFS")	0	0	(777)
Proceeds from sales of LHFS	0	0	16,423
Amortization and accretion of premiums and discounts on securities	1,661	1,242	3,150
Depreciation and amortization of premises and equipment	9,133	9,143	8,458
Amortization of intangible assets	1,964	2,316	234
Amortization of deferred amounts related to FHLB advances, net	539	8	1,173
Common stock committed to be released for allocation - ESOP	1,988	2,200	2,193
Stock-based compensation	570	552	372
Provision for deferred income taxes	(5,588)	(361)	(4,540)
Changes in:
Unrestricted cash collateral (provided to)/received from derivative counterparties, net	0	(9,970)	10,701
Other assets, net	9,105	6,220	1,712
Income taxes payable/receivable, net	774	2,173	(2,262)
Accounts payable and accrued expenses	(8,231)	(19,746)	(639)
Net cash provided by operating activities	92,928	80,947	124,163
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of AFS securities	(1,007,763)	(386,702)	(411,459)
Proceeds from calls, maturities and principal reductions of AFS securities	667,952	359,551	192,966
Proceeds from calls, maturities and principal reductions of HTM securities	0	165,336	212,267
Proceeds from sale of AFS securities	0	0	2,078
Proceeds from the redemption of FHLB stock	10,421	197,054	291,506
Purchase of FHLB stock	0	(187,961)	(277,552)
Net change in loans receivable	191,359	95,358	(37,537)
Purchase of premises and equipment	(14,742)	(11,732)	(11,761)
Proceeds from sale of other real estate owned ("OREO")	993	2,053	2,240
Cash acquired from acquisition	0	0	15,685
Proceeds from the redemption of common equity securities related to the redemption of junior subordinated debentures	0	302	0
Proceeds from bank-owned life insurance ("BOLI") death benefit	490	0	0
Net cash (used in) provided by investing activities	(151,290)	233,259	(21,567)
CASH FLOWS FROM FINANCING ACTIVITIES:
Cash dividends paid	(93,862)	(134,929)	(118,312)
Net change in deposits	609,541	(21,487)	(58,988)
Proceeds from borrowings	1,665,600	5,518,700	17,275,100
Repayments on borrowings	(2,112,600)	(5,563,752)	(17,414,200)
Change in advance payments by borrowers for taxes and insurance	35	422	939
Payment of FHLB prepayment penalties	(4,215)	0	0
Repurchase of common stock	(20,767)	0	0
Stock options exercised	638	1,485	261
Net cash provided by (used in) financing activities	44,370	(199,561)	(315,200)
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, RESTRICTED CASH AND RESTRICTED CASH EQUIVALENTS	(13,992)	114,645	(212,604)
CASH, CASH EQUIVALENTS, RESTRICTED CASH AND RESTRICTED CASH EQUIVALENTS:
Beginning of year	253,700	139,055	351,659
End of year	239,708	253,700	139,055
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Income tax payments	13,045	17,779	24,785
Interest payments	118,610	123,508	119,699
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Loans transferred to LHFS	0	0	15,814
Operating lease right-of-use assets obtained	16,841	0	0
Operating lease liabilities obtained	16,726	0	0
Common stock issued	0	0	39,113
Fair value of assets acquired, excluding acquired cash and intangibles	0	0	418,062
Fair value of liabilities assumed	0	0	412,675
Transfer of HTM securities, at amortized cost, to AFS securities	$ 0	$ 444,732	$ 0