Allowance for Losses on Loans - Activity in Allowance for Loan Losses by Loan Portfolio Segment and Class (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	$ 177,420	$ 171,384	$ 172,808	$ 171,300
Charge-offs	(10,543)	(281)	(16,897)	(1,870)
Recoveries	192	876	1,158	5,049
Provisions & Transfers	11,000	(1,000)	21,000	(3,500)
Ending Allowance	178,069	170,979	178,069	170,979
Provision & Transfers	9,000	1,500	15,000	1,500
Unfunded Commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions & Transfers	(2,000)	2,500	(6,000)	5,000
Commercial loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	137,665	129,440	133,476	125,375
Charge-offs	(10,469)	(28)	(16,605)	(1,475)
Recoveries	34	42	143	3,122
Provisions & Transfers	10,955	1,405	21,171	3,837
Ending Allowance	138,185	130,859	138,185	130,859
Commercial loans \| Multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	13,038	14,463	12,013	16,949
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions & Transfers	(62)	(1,889)	963	(4,375)
Ending Allowance	12,976	12,574	12,976	12,574
Commercial loans \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	27,803	24,682	25,814	23,437
Charge-offs	0	0	0	(529)
Recoveries	0	23	5	820
Provisions & Transfers	329	595	2,313	1,572
Ending Allowance	28,132	25,300	28,132	25,300
Commercial loans \| Commercial & industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	63,301	53,903	57,210	45,957
Charge-offs	(10,469)	(27)	(16,605)	(943)
Recoveries	10	8	84	72
Provisions & Transfers	9,073	1,040	21,226	9,838
Ending Allowance	61,915	54,924	61,915	54,924
Commercial loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	26,027	22,707	26,161	25,585
Charge-offs	0	0	0	0
Recoveries	0	0	0	2,179
Provisions & Transfers	1,889	3,127	1,755	(1,930)
Ending Allowance	27,916	25,834	27,916	25,834
Commercial loans \| Land - acquisition & development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	7,496	13,685	12,278	13,447
Charge-offs	0	(1)	0	(3)
Recoveries	24	11	54	51
Provisions & Transfers	(274)	(1,468)	(5,086)	(1,268)
Ending Allowance	7,246	12,227	7,246	12,227
Consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	39,755	41,944	39,332	45,925
Charge-offs	(74)	(253)	(292)	(395)
Recoveries	158	834	1,015	1,927
Provisions & Transfers	45	(2,405)	(171)	(7,337)
Ending Allowance	39,884	40,120	39,884	40,120
Consumer loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	3,456	3,129	3,410	4,907
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions & Transfers	(235)	225	(189)	(1,553)
Ending Allowance	3,221	3,354	3,221	3,354
Consumer loans \| Single-family residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	26,916	28,992	25,518	30,978
Charge-offs	0	0	(34)	0
Recoveries	18	252	552	804
Provisions & Transfers	149	(3,027)	1,047	(5,565)
Ending Allowance	27,083	26,217	27,083	26,217
Consumer loans \| Land - consumer lot loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	3,945	5,105	5,047	4,939
Charge-offs	0	0	0	(27)
Recoveries	9	2	14	47
Provisions & Transfers	(184)	113	(1,291)	261
Ending Allowance	3,770	5,220	3,770	5,220
Consumer loans \| HELOC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	2,662	2,475	2,482	2,390
Charge-offs	0	0	0	0
Recoveries	0	249	1	350
Provisions & Transfers	81	(92)	260	(108)
Ending Allowance	2,743	2,632	2,743	2,632
Consumer loans \| Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	2,776	2,243	2,875	2,711
Charge-offs	(74)	(253)	(258)	(368)
Recoveries	131	331	448	726
Provisions & Transfers	234	376	2	(372)
Ending Allowance	$ 3,067	$ 2,697	$ 3,067	$ 2,697

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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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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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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Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. 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 (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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Financing Receivable, Allowance For Credit Losses, Provisions and Transfers

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