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Loans Receivable and Allowance for Credit Losses on Loans (Details Textual) Details http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-tables 62 false false R63.htm 995605 - Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Portfolio Loan Composition (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-schedule-of-portfolio-loan-composition-details Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Portfolio Loan Composition (Details) Details 63 false false R64.htm 995606 - Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Allowance for Credit Losses by Category (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-schedule-of-allowance-for-credit-losses-by-category-details Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Allowance for Credit Losses by Category (Details) Details 64 false false R65.htm 995607 - Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Modified Financing Receivables (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-schedule-of-modified-financing-receivables-details Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Modified Financing Receivables (Details) Details 65 false false R66.htm 995608 - Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Financing Receivable, Modified, Past Due (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-schedule-of-financing-receivable-modified-past-due-details Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - 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Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Amortized Cost of Nonaccrual Loans (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-schedule-of-amortized-cost-of-nonaccrual-loans-details Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Amortized Cost of Nonaccrual Loans (Details) Details 69 false false R70.htm 995612 - Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Collateral Dependent Loans (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-3-loans-receivable-and-allowance-for-credit-losses-on-loans-schedule-of-collateral-dependent-loans-details Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Collateral Dependent Loans (Details) Details 70 false false R71.htm 995613 - Disclosure - Note 3 - Loans Receivable and Allowance for Credit Losses on Loans - 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Disclosure - Note 6 - Leases (Details Textual) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-6-leases-details-textual Note 6 - Leases (Details Textual) Details http://investorrelations.fsbwa.com/20251231/role/statement-note-6-leases-tables 77 false false R78.htm 995620 - Disclosure - Note 6 - Leases - Schedule of Lease Cost (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-6-leases-schedule-of-lease-cost-details Note 6 - Leases - Schedule of Lease Cost (Details) Details 78 false false R79.htm 995621 - Disclosure - Note 6 - Leases - Schedule of Supplemental Information (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-6-leases-schedule-of-supplemental-information-details Note 6 - Leases - Schedule of Supplemental Information (Details) Details 79 false false R80.htm 995622 - Disclosure - Note 6 - Leases - Schedule of Maturity for Operating Leases (Details) Sheet http://investorrelations.fsbwa.com/20251231/role/statement-note-6-leases-schedule-of-maturity-for-operating-leases-details Note 6 - 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