Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	$ 172,808	$ 171,300
Charge-offs	(46,470)	(2,139)
Recoveries	1,369	5,647
Provision & Transfers	49,500	(2,000)
Ending allowance	177,207	172,808
Commercial loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	133,476	125,375
Charge-offs	(45,856)	(1,742)
Recoveries	274	3,306
Provision & Transfers	49,300	6,537
Ending allowance	137,194	133,476
Commercial loans \| Multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	12,013	16,949
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	1,142	(4,936)
Ending allowance	13,155	12,013
Commercial loans \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	25,814	23,437
Charge-offs	0	(529)
Recoveries	103	984
Provision & Transfers	2,925	1,922
Ending allowance	28,842	25,814
Commercial loans \| Commercial & industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	57,210	45,957
Charge-offs	(45,856)	(1,202)
Recoveries	93	73
Provision & Transfers	47,326	12,382
Ending allowance	58,773	57,210
Commercial loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	26,161	25,585
Charge-offs	0	0
Recoveries	0	2,179
Provision & Transfers	3,247	(1,603)
Ending allowance	29,408	26,161
Commercial loans \| Land - acquisition & development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	12,278	13,447
Charge-offs	0	(11)
Recoveries	78	70
Provision & Transfers	(5,340)	(1,228)
Ending allowance	7,016	12,278
Consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	39,332	45,925
Charge-offs	(614)	(397)
Recoveries	1,095	2,341
Provision & Transfers	200	(8,537)
Ending allowance	40,013	39,332
Consumer loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	3,410	4,907
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	(629)	(1,497)
Ending allowance	2,781	3,410
Consumer loans \| Single-family residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	25,518	30,978
Charge-offs	(34)	0
Recoveries	568	1,002
Provision & Transfers	1,977	(6,462)
Ending allowance	28,029	25,518
Consumer loans \| Land - consumer lot loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	5,047	4,939
Charge-offs	0	(27)
Recoveries	23	48
Provision & Transfers	(1,558)	87
Ending allowance	3,512	5,047
Consumer loans \| HELOC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	2,482	2,390
Charge-offs	0	0
Recoveries	2	351
Provision & Transfers	375	(259)
Ending allowance	2,859	2,482
Consumer loans \| Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	2,875	2,711
Charge-offs	(580)	(370)
Recoveries	502	940
Provision & Transfers	35	(406)
Ending allowance	$ 2,832	$ 2,875

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
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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- Definition

Financing Receivable, Allowance for Credit Losses, Provision and Transfers

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