Loans Receivable - Schedule of Loan Modifications (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 117,444	$ 93,799
% of Total Loan Class Balance	0.07%	0.26%	0.38%	0.28%
Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 2,577	$ 55,937	$ 63,066	$ 58,250
Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 12,559	$ 0	13,595	0
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 106,855	$ 92,474
% of Total Loan Class Balance	0.05%	0.46%	0.54%	0.47%
Commercial loans \| Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 2,577	$ 55,937	$ 63,066	$ 57,797
Weighted average term extension	5 months	10 months	10 months	10 months
Commercial loans \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 3,006	$ 0	$ 3,006	$ 0
Deferral Amount	$ 167	$ 0	167	0
Commercial loans \| Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 19,801	$ 1,099
% of Total Loan Class Balance	0.00%	0.02%	0.00%	0.02%
Commercial loans \| Multi-family \| Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 0	$ 1,098	$ 0	$ 1,098
Weighted average term extension	0 months	3 months	0 months	3 years
Commercial loans \| Multi-family \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 0	$ 0	$ 0	$ 0
Deferral Amount	$ 0	$ 0	0	0
Commercial loans \| Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 51,195	$ 28,607
% of Total Loan Class Balance	0.13%	0.15%	0.99%	0.15%
Commercial loans \| Commercial real estate \| Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 1,700	$ 5,393	$ 33,190	$ 5,393
Weighted average term extension	3 months	24 months	8 months	24 months
Commercial loans \| Commercial real estate \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 3,006	$ 0	$ 3,006	$ 0
Deferral Amount	$ 167	$ 0	167	0
Commercial loans \| Commercial & industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 30,471	$ 57,380
% of Total Loan Class Balance	0.03%	2.07%	1.07%	2.15%
Commercial loans \| Commercial & industrial \| Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 877	$ 49,446	$ 29,876	$ 51,306
Weighted average term extension	9 months	9 months	11 months	9 months
Commercial loans \| Commercial & industrial \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 0	$ 0	$ 0	$ 0
Deferral Amount	$ 0	$ 0	0	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 10,589	$ 1,325
% of Total Loan Class Balance	0.12%	0.00%	0.13%	0.01%
Consumer loans \| Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 0	$ 0	$ 0	$ 453
Weighted average term extension	0 months	0 months	0 months	6 months
Consumer loans \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 9,553	$ 0	$ 10,589	$ 0
Deferral Amount	$ 285	$ 0	306	0
Consumer loans \| Single-family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount			$ 10,589	$ 1,325
% of Total Loan Class Balance	0.13%	0.00%	0.14%	0.01%
Consumer loans \| Single-family residential \| Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 0	$ 0	$ 0	$ 453
Weighted average term extension	0 months	0 months	0 months	6 months
Consumer loans \| Single-family residential \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in period, amount	$ 9,553	$ 0	$ 10,589	$ 0
Deferral Amount	$ 285	$ 0	$ 306	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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