Allowance for Losses on Loans - Schedule of Activity in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025	Sep. 30, 2025
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	$ 199,539	$ 204,522	$ 199,720	$ 203,753	$ 203,753
Charge-offs	(805)	(5,443)	(5,325)	(6,228)
Recoveries	216	380	1,055	934
Provision & Transfers	3,000	3,250	6,500	4,250
Ending Allowance	201,950	202,709	201,950	202,709	199,720
Provision (recapture)	3,000	3,250	6,500	4,250
Commercial loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	155,747	152,468	152,134	153,373	153,373
Charge-offs	(343)	(4,628)	(4,539)	(5,148)	(11,498)
Recoveries	152	215	914	230
Provision & Transfers	4,936	3,226	11,983	2,826
Ending Allowance	160,492	151,281	160,492	151,281	152,134
Provision (recapture)	4,936	3,226	11,983	2,826
Commercial loans \| Multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	25,843	25,997	25,953	25,248	25,248
Charge-offs	(81)	0	(81)	0	(555)
Recoveries	0	0	0	0
Provision & Transfers	161	559	51	1,308
Ending Allowance	25,923	26,556	25,923	26,556	25,953
Provision (recapture)	161	559	51	1,308
Commercial loans \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	42,105	37,873	41,988	39,210	39,210
Charge-offs	0	(4,392)	0	(4,555)	(9,652)
Recoveries	7	169	655	169
Provision & Transfers	(609)	4,819	(1,140)	3,645
Ending Allowance	41,503	38,469	41,503	38,469	41,988
Provision (recapture)	(609)	4,819	(1,140)	3,645
Commercial loans \| Commercial & industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	62,102	60,474	59,163	58,748	58,748
Charge-offs	(262)	(236)	(4,458)	(593)	(1,291)
Recoveries	138	38	143	42
Provision & Transfers	6,684	(129)	13,814	1,950
Ending Allowance	68,662	60,147	68,662	60,147	59,163
Provision (recapture)	6,684	(129)	13,814	1,950
Commercial loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	18,475	20,903	18,136	22,267	22,267
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision & Transfers	(1,763)	(1,497)	(1,424)	(2,861)
Ending Allowance	16,712	19,406	16,712	19,406	18,136
Provision (recapture)	(1,763)	(1,497)	(1,424)	(2,861)
Commercial loans \| Land - acquisition & development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	7,222	7,221	6,894	7,900	7,900
Charge-offs	0	0	0	0
Recoveries	7	8	116	19
Provision & Transfers	463	(526)	682	(1,216)
Ending Allowance	7,692	6,703	7,692	6,703	6,894
Provision (recapture)	463	(526)	682	(1,216)
Consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	43,792	52,054	47,586	50,380	50,380
Charge-offs	(462)	(815)	(786)	(1,080)	(1,672)
Recoveries	64	165	141	704
Provision & Transfers	(1,936)	24	(5,483)	1,424
Ending Allowance	41,458	51,428	41,458	51,428	47,586
Provision (recapture)	(1,936)	24	(5,483)	1,424
Consumer loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	455	1,219	610	1,427	1,427
Charge-offs	0	0	0	0
Recoveries	2	0	4	0
Provision & Transfers	(155)	(143)	(312)	(351)
Ending Allowance	302	1,076	302	1,076	610
Provision (recapture)	(155)	(143)	(312)	(351)
Consumer loans \| Single-family residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	35,847	42,117	38,880	40,523	40,523
Charge-offs	(31)	(338)	(82)	(338)	(338)
Recoveries	6	7	12	463
Provision & Transfers	(2,143)	(823)	(5,131)	315
Ending Allowance	33,679	40,963	33,679	40,963	38,880
Provision (recapture)	(2,143)	(823)	(5,131)	315
Consumer loans \| Land - consumer lot loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	1,958	2,527	2,104	2,564	2,564
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision & Transfers	(137)	(112)	(283)	(149)
Ending Allowance	1,821	2,415	1,821	2,415	2,104
Provision (recapture)	(137)	(112)	(283)	(149)
Consumer loans \| HELOC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	2,951	3,158	3,069	3,049	3,049
Charge-offs	0	0	0	0
Recoveries	1	0	1	2
Provision & Transfers	(102)	99	(220)	206
Ending Allowance	2,850	3,257	2,850	3,257	3,069
Provision (recapture)	(102)	99	(220)	206
Consumer loans \| Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	2,581	3,033	2,923	2,817	2,817
Charge-offs	(431)	(477)	(704)	(742)	(1,334)
Recoveries	55	158	124	239
Provision & Transfers	601	1,003	463	1,403
Ending Allowance	2,806	3,717	2,806	3,717	$ 2,923
Provision (recapture)	601	1,003	463	1,403
Unfunded commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision & Transfers	1,000	(500)	1,000	(1,500)
Provision (recapture)	$ 1,000	$ (500)	$ 1,000	$ (1,500)

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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+ 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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+ References

Reference 1: 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

Reference 2: 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

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