Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	$ 171,300	$ 166,955
Charge-offs	(2,139)	(425)
Recoveries	5,647	6,770
Provision & Transfers	(2,000)	(2,000)
Ending allowance	172,808	171,300
Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	171,300
Ending allowance		171,300
Commercial loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	125,375	109,923
Charge-offs	(1,742)	(33)
Recoveries	3,306	3,503
Provision & Transfers	6,537	11,982
Ending allowance	133,476	125,375
Commercial loans \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	125,375
Ending allowance		125,375
Commercial loans \| Multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	16,949	13,853
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	(4,936)	3,096
Ending allowance	12,013	16,949
Commercial loans \| Multi-family \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	16,949
Ending allowance		16,949
Commercial loans \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	23,437	22,516
Charge-offs	(529)	0
Recoveries	984	2,789
Provision & Transfers	1,922	(1,868)
Ending allowance	25,814	23,437
Commercial loans \| Commercial real estate \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	23,437
Ending allowance		23,437
Commercial loans \| Commercial & industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	45,957	38,665
Charge-offs	(1,202)	(31)
Recoveries	73	92
Provision & Transfers	12,382	7,231
Ending allowance	57,210	45,957
Commercial loans \| Commercial & industrial \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	45,957
Ending allowance		45,957
Commercial loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	25,585	24,156
Charge-offs	0	0
Recoveries	2,179	0
Provision & Transfers	(1,603)	1,429
Ending allowance	26,161	25,585
Commercial loans \| Construction \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	25,585
Ending allowance		25,585
Commercial loans \| Land - acquisition & development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	13,447	10,733
Charge-offs	(11)	(2)
Recoveries	70	622
Provision & Transfers	(1,228)	2,094
Ending allowance	12,278	13,447
Commercial loans \| Land - acquisition & development \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	13,447
Ending allowance		13,447
Consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	45,925	57,032
Charge-offs	(397)	(392)
Recoveries	2,341	3,267
Provision & Transfers	(8,537)	(13,982)
Ending allowance	39,332	45,925
Consumer loans \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	45,925
Ending allowance		45,925
Consumer loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	4,907	3,555
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	(1,497)	1,352
Ending allowance	3,410	4,907
Consumer loans \| Construction \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	4,907
Ending allowance		4,907
Consumer loans \| Single-family residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	30,978	45,186
Charge-offs	0	(106)
Recoveries	1,002	2,026
Provision & Transfers	(6,462)	(16,128)
Ending allowance	25,518	30,978
Consumer loans \| Single-family residential \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	30,978
Ending allowance		30,978
Consumer loans \| Land - consumer lot loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	4,939	2,729
Charge-offs	(27)	0
Recoveries	48	168
Provision & Transfers	87	2,042
Ending allowance	5,047	4,939
Consumer loans \| Land - consumer lot loans \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	4,939
Ending allowance		4,939
Consumer loans \| HELOC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	2,390	2,571
Charge-offs	0	0
Recoveries	351	52
Provision & Transfers	(259)	(233)
Ending allowance	2,482	2,390
Consumer loans \| HELOC \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	2,390
Ending allowance		2,390
Consumer loans \| Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	2,711	2,991
Charge-offs	(370)	(286)
Recoveries	940	1,021
Provision & Transfers	(406)	(1,015)
Ending allowance	2,875	2,711
Consumer loans \| Consumer \| Adjusted
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	$ 2,711
Ending allowance		$ 2,711

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
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