Document And Entity Information
Due after ten years, fair value
Note To Financial Statement Details Textual
Total amounts presented on the Consolidated Statements of Income
Significant Accounting Policies
Subtotal, amortized cost
Note 2 - Business Combination
Due within one year, amortized cost
Note 3 - Investments
Subtotal, fair value
Note 4 - Loans Receivable and Allowance for Credit Losses - Loans
Due within one year, fair value
Note 5 - Mortgage Servicing Rights
Due after one year through five years, fair value
Note 6 - Derivatives
Due after five years through ten years, fair value
Note 7 - Leases
Collateralized Mortgage-Backed Securities [Member]
Note 8 - Other Real Estate Owned ("OREO")
Note 9 - Deposits
Note 10 - Commitments and Contingencies
Note 11 - Fair Value Measurements
Note 12 - Earnings Per Share
Note 13 - Stock-based Compensation
Note 14 - Regulatory Capital
Note 15 - Business Segments
Note 16 - Goodwill and Other Intangible Assets
Note 17 - Revenue From Contracts With Customers
Commercial Real Estate [Member]
us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term (Year)
Note 2 - Business Combination - Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details)
Note 3 - Investments - Schedule of Amortized Costs and Fair Values of Securities (Details)
Note 3 - Investments - Schedule of Debt Securities, Held-to-Maturity, Allowance for Credit Loss Roll Forward (Details)
Note 3 - Investments - Schedule of Debt Securities, Held-to-Maturity Credit Quality Indicators (Details)
Note 3 - Investments - Schedule of Securities Pledged as Collateral (Details)
US States and Political Subdivisions Debt Securities [Member]
Note 3 - Investments - Schedule of Investments in Unrealized Loss Position (Details)
Note 3 - Investments - Schedule of Contractual Maturities (Details)
Commercial Loan [Member]
Note 3 - Investments - Schedule of Gain or Loss of Securities (Details)
Residential Mortgage [Member]
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Portfolio Loan Composition (Details)
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Allowance for Credit Losses by Category (Details)
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Loan Modifications to Borrowers Experiencing Financial Difficulty (Details)
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Past Due Loans (Details)
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Risk Rated Loan by Category (Details)
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Amortized Cost of Nonaccrual Loans (Details)
Granted, Weighted Average Grant Date Fair Value (in dollars per share)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
12 months or longer, unrealized loss, available for sale securities
Note 4 - Loans Receivable and Allowance for Credit Losses on Loans - Schedule of Collateral Dependent Loans (Details)
Less vested, Weighted Average Grant Date Fair Value (in dollars per share)
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Available for sale securities, unrealized losses total
Note 5 - Mortgage Servicing Rights - Schedule of Mortgage Servicing Rights (Details)
Less forfeited, Weighted Average Grant Date Fair Value (in dollars per share)
Note 5 - Mortgage Servicing Rights - Valuation Assumptions (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
Beginning balance, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share)
Ending balance, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share)
Note 5 - Mortgage Servicing Rights - Schedule of Sensitivity Analysis of Fair Value (Details)
Less forfeited, RSA (in shares)
Note 6 - Derivatives - Schedule of Fair Value Hedges Cumulative-basis Adjustment (Details)
Note 6 - Derivatives - Schedule of Derivative Instruments (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Beginning balance, RSA (in shares)
Ending balance, RSA (in shares)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Less than 12 months, unrealized loss, available for sale securities
Note 6 - Derivatives - Schedule of Hedging Relationship (Details)
fsbw_PaymentsForOriginationOfLoansAndPrincipleCollectionsNet
Portfolio loan originations and principal collections, net
The amount of cash paid for the origination of loans net of principle collections.
Note 6 - Derivatives - Schedule of Offsetting of Derivative Assets (Details)
US Government Agencies Debt Securities [Member]
Note 6 - Derivatives - Schedule of Offsetting of Derivative Liabilities (Details)
Note 7 - Leases - Schedule of Lease Cost (Details)
Granted, RSA (in shares)
Change in fair value on portfolio loans measured under the fair value option
Amount of unrealized gain (loss) on portfolio loans measured under the fair value option.
Corporate Debt Securities [Member]
Note 7 - Leases - Schedule of Supplemental Information (Details)
Less vested, RSA (in shares)
Note 7 - Leases - Schedule of Maturity for Operating Leases (Details)
Expected to vest, Weighted Average Remaining Contractual Term (Year)
Note 8 - Other Real Estate Owned ("OREO") - Schedule of Other Real Estate Owned (Details)
Note 9 - Deposits - Schedule of Deposit Liabilities (Details)
Note 9 - Deposits - Schedule of Maturity (Details)
Exercisable, Intrinsic Value
Note 9 - Deposits - Schedule Interest Expense by Category (Details)
fsbw_GainLossOnSaleOfLoansHeldForSale
Gain on sale of loans held for sale
The amount of gain or loss on the sale of loans held for sale.
Note 10 - Commitments and Contingencies - Schedule of Commitments (Details)
Expected to vest, options (in shares)
Note 11 - Fair Value Measurements - Schedule of Financial Assets and Liabilities on a Recurring Basis (Details)
Expected to vest, Weighted Average Exercise Price (in dollars per share)
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
Note 11 - Fair Value Measurements - Schedule of Financial Assets on a Non-recurring Basis (Details)
Expected to vest, Intrinsic Value
Note 11 - Fair Value Measurements - Schedule of Schedule of Financial Assets and Liabilities on a Recurring and Non-recurring Basis (Details)
Exercisable, Weighted Average Exercise Price (in dollars per share)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions
Note 11 - Fair Value Measurements - Schedule of Reconciliation of Financial Assets and Liabilities with Unobservable Inputs (Details)
Exercisable, Weighted Average Remaining Contractual Term (Year)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions
Note 11 - Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments (Details)
Note 12 - Earnings Per Share - Schedule of Earnings Per Share (Details)
Available for sale securities, fair value, total
Note 13 - Stock-based Compensation - Schedule of Stock Option Awards (Details)
Note 13 - Stock-based Compensation - Schedule of Stock Option Awards (Details) (Parentheticals)
Less exercised, Intrinsic Value
Note 13 - Stock-based Compensation - Schedule of Restricted Stock Awards (Details)
Exercisable, options (in shares)
Note 14 - Regulatory Capital - Schedule of Comparison (Details)
Note 15 - Business Segments - Schedule of Segment Financial Results (Details)
Note 16 - Goodwill and Other Intangible Assets - Schedule of Changes in Intangible Assets (Details)
Outstanding, Weighted Average Remaining Contractual Term (Year)
Note 16 - Goodwill and Other Intangible Assets - Schedule of Amortization (Details)
Less than 12 months, fair value, available for sale securities
Outstanding, Intrinsic Value
Note 17 - Revenue From Contracts With Customers - Schedule of Noninterest Income (Details)
12 months or longer, unrealized loss, fair value, available for sale securities
Notes To Financial Statements
Notes To Financial Statements [Abstract]
Financial Instruments [Domain]
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Beginning balance, Weighted Average Exercise Price (in dollars per share)
Ending balance, Weighted Average Exercise Price (in dollars per share)
Deposits [Member]
Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block]
Less forfeited, Weighted Average Exercise Price (in dollars per share)
Financial Instrument [Axis]
us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Financing Receivable, Modified, Commitment to Lend
Granted, Weighted Average Exercise Price (in dollars per share)
Without single maturity date, fair value
Less exercised, Weighted Average Exercise Price (in dollars per share)
Lessee, Operating Leases [Text Block]
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
Without single maturity date, amortized cost
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Beginning balance, options (in shares)
Ending balance, options (in shares)
us-gaap_PolicyTextBlockAbstract
Accounting Policies
Realized gain
Change in fair value on available-for-sale investment securities
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)
us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss
Realized loss
us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)
us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage
LIABILITIES
Vesting [Axis]
Vesting [Domain]
Share-Based Payment Arrangement, Tranche One [Member]
us-gaap_Assets
TOTAL ASSETS
Plan Name [Axis]
Plan Name [Domain]
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)
Deferred tax asset, net
Share-Based Payment Arrangement [Text Block]
Other assets
Award Type [Domain]
Basis of Presentation and Significant Accounting Policies [Text Block]
Award Type [Axis]
Balance, accumulated amortization
Balance, accumulated amortization
us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Core deposit intangible, net
Total
Balance, net
Balance, net
us-gaap_FiniteLivedIntangibleAssetsGross
Balance
Balance
us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfOtherThan10Or20PercentAdverseChangeInOtherAssumptionPercent
Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Other than 10 or 20 Percent Adverse Change in Other Assumption, Percent
Bank Servicing [Member]
Commitments and Contingencies Disclosure [Text Block]
Premises and equipment, net
Goodwill
Goodwill
Schedule of Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets [Table Text Block]
us-gaap_DerivativeFairValueOfDerivativeLiability
Derivative Liability, Before Offset
Financing Receivable, Gross
Financing Receivable, before Allowance for Credit Loss
us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue
Change in cash surrender value of BOLI
Derivative Asset, Before Offset
Derivative Asset
Derivative asset
Derivative Instrument [Axis]
Derivative Contract [Domain]
Federal Home Loan Bank Advances [Member]
Fair value, available for sale securities
Securities available-for-sale, at fair value (amortized cost of $309,959 and $328,695, net of allowance for credit losses of $0 and $0, respectively)
Amortized cost, held to maturity securities
us-gaap_HeldToMaturitySecurities
Debt Securities, Held-to-Maturity, Amortized Cost
Impairment of MSRs
us-gaap_ServicingAssetAtAmortizedValueOtherChangesThatAffectBalanceAmount
us-gaap_ServicingAssetAtAmortizedValueAdditions
Additions
us-gaap_ServicingAssetAtAmortizedValueDisposals
Sales
us-gaap_ServicingAssetAtAmortizedValueAmortization1
MSRs amortized
Servicing Asset at Amortized Cost [Table Text Block]
PROVISION FOR INCOME TAXES
Provision for income taxes
Conditional prepayment rate
Weighted average life in years (Year)
us-gaap_MortgageLoansInProcessOfForeclosureAmount
Mortgage Loans in Process of Foreclosure, Amount
Discount rate
Gain (Loss) on Securities [Table Text Block]
Other Real Estate, Roll Forward [Table Text Block]
us-gaap_OtherRealEstateAdditions
Additions
Due after five years through ten years, amortized cost, held to maturity
Total securities held-to-maturity, amortized cost
Interest-bearing deposits at other financial institutions
Due after five years through ten years, fair value, held to maturity
us-gaap_CashAndCashEquivalentsAtCarryingValue
Total cash and cash equivalents
us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Gross unrealized losses, held to maturity securities
Gross unrealized gains, held to maturity securities
Salaries and benefits
Schedule of Servicing Assets at Fair Value [Table Text Block]
Cash and due from banks
Total securities held-to-maturity, fair value
Certificates of deposit at other financial institutions
Certificates of deposit at other financial institutions
Transfers and Servicing of Financial Assets [Text Block]
Real Estate Owned [Text Block]
Amendment Flag
City Area Code
Investment Securities, Fair Value
New Accounting Pronouncements, Policy [Policy Text Block]
Gain on sale of loans held for sale
Net Amount [Member]
Related to net amount.
Current Fiscal Year End Date
Net interest income recognized on cash flows of derivatives designated as hedging instruments
The amount of net interest income (expense) recognized on cash flow of derivatives designated as hedging instruments.
Loans receivable, net of allowance for credit losses of $31,479 and $31,534 (includes $15,003 and $15,088 of loans at fair value, respectively)
Total loans receivable, net
Loss on sale of investment securities
Loss on sale of investment securities
us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss
Debt Securities, Available-for-Sale, Realized Gain (Loss)
Interest Receivable
Accrued interest receivable
Document Fiscal Period Focus
Document Fiscal Year Focus
Consolidation, Policy [Policy Text Block]
us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net
Document Period End Date
Entity File Number
Actual, Tier 1 Leverage Rate
Banking Regulation, Tier 1 Leverage Capital Ratio, Actual
Capital Adequacy, Tier 1 Leverage Rate
Entity Emerging Growth Company
Well Capitalized, Tier 1 Leverage Rate
Document Type
us-gaap_SecuritiesReceivedAsCollateral
Securities Received as Collateral
Investment Securities, Cost
Well Capitalized, Total Capital Rate
Entity Small Business
Entity Shell Company
Actual, CET 1 Rate
Banking Regulation, Common Equity Tier 1 Risk-Based Capital Ratio, Actual
Document Information [Line Items]
Document Information [Table]
Actual, Capital, Rate
Banking Regulation, Total Risk-Based Capital Ratio, Actual
Capital Adequacy, Total Rate
Entity Filer Category
Actual, Tier 1 Risk-based Rate
Banking Regulation, Tier 1 Risk-Based Capital Ratio, Actual
Entity Current Reporting Status
Capital Adequacy, Tier 1 Risk-based Rate
Acquisition costs
Well Capitalized, Tier 1 Risk-based Rate
us-gaap_ImpairmentOfIntangibleAssetsFinitelived
Impairment of Intangible Assets, Finite-Lived
Actual, Capital
Capital Adequacy, Total
Well Capitalized, Total Capital
us-gaap_NumberOfRealEstateProperties
Number of Real Estate Properties
Real Estate Property Ownership [Axis]
Bank owned life insurance (“BOLI”), net
Real Estate Properties [Domain]
Actual, Tier 1 Leverage
us-gaap_GoodwillImpairmentLoss
Goodwill, Impairment Loss
Capital Adequacy, Tier 1 Leverage
Well Capitalized, Tier 1 Leverage
Fair value MSRs
Servicing Asset at Fair Value, Amount
Actual, CET 1
Statement of Comprehensive Income [Abstract]
us-gaap_ServicingAssetAtAmortizedValue
Balance, MSR
Balance, MSR
Capital Adequacy, CET 1
Entity Tax Identification Number
Mortgage servicing rights (“MSRs”), held at the lower of cost or fair value
Well Capitalized, CET 1
Entity Central Index Key
Actual, Tier 1 Risk-based
Entity Registrant Name
Capital Adequacy, Tier 1 Risk-based
Well Capitalized, Tier 1 Risk-based
Entity [Domain]
Legal Entity [Axis]
Entity Address, Address Line One
Financing Receivable, Allowance for Credit Loss
Financing Receivable, Allowance for Credit Loss
ACL on loans
Amortization of core deposit intangible
us-gaap_AmortizationOfIntangibleAssets
Amortization of Intangible Assets
Amortization
ecd_NonRule10b51ArrTrmntdFlag
Non-Rule 10b5-1 Arrangement Terminated [Flag]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]
Entity Address, City or Town
ecd_Rule10b51ArrTrmntdFlag
Rule 10b5-1 Arrangement Terminated [Flag]
ecd_Rule10b51ArrAdoptedFlag
Rule 10b5-1 Arrangement Adopted [Flag]
Entity Address, Postal Zip Code
Regulatory Capital Requirements under Banking Regulations [Text Block]
us-gaap_OtherRealEstate
Balance, OREO
Balance, OREO
Entity Address, State or Province
ecd_NonRule10b51ArrAdoptedFlag
Non-Rule 10b5-1 Arrangement Adopted [Flag]
Material Terms of Trading Arrangement [Text Block]
us-gaap_GainLossOnCashFlowHedgeIneffectivenessNet
Net income recognized on cash flow hedges
Number of Employees, Geographic Area [Member]
Entity Common Stock, Shares Outstanding
Municipal Bonds [Member]
Marketing and advertising
Professional and board fees
Securities Investment [Member]
Trading Symbol
Concentration Risk Benchmark [Axis]
Concentration Risk Benchmark [Domain]
Data processing
Occupancy
Cumulative Amount of Fair Value Hedging Adjustment
us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease)
Local Phone Number
us-gaap_TableTextBlock
Notes Tables
Hedged Assets
(Disbursements) proceeds from stock options exercised, net
The amount of proceeds (disbursements) from stock options exercised.
Savings and money market
The aggregate interest expense incurred on the following for deposits in domestic offices: (1) money market deposits and (2) savings deposits.
fsbw_GoodwillAmorizationPeriodForDeductibleTaxPurposes
Goodwill, Amorization Period for Deductible Tax Purposes (Year)
The goodwill amortization period for deductible tax purposes.
Operations
fsbw_SubordinatedDebtNetOfUnamortizedDebtIssuanceExpense
Total subordinated notes less unamortized debt issuance costs
Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer), net of unamortized debt issuance expense. Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.
Allocated Overhead Expense [Member]
Related to allocated overhead expense.
fsbw_NumberOfBankBranches
Number of Bank Branches
Represents the number bank branches.
Federal Home Loan Bank (“FHLB”) stock, at cost
FHLB stock, at cost
Retention in gross MSRs from loan sales
Represents the retention of mortgage servicing rights from loan sales.
Columbia State Bank [Member]
Information pertaining to the branch purchase agreement.
Securities held-to-maturity, at fair value
Anchor Bank [Member]
Information pertaining to Anchor Bank.
Bank of America [Member]
Information pertaining to bank branches acquired.
us-gaap_CustodyFees
Custody Fees
Derivative Instruments, Gain (Loss) [Table Text Block]
us-gaap_InterestExpense
Total interest expense
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Certificates of deposit
us-gaap_DerivativeLiabilityFairValueGrossAssetAndRightToReclaimCashOffset
Derivative liability, offset
Interest-bearing checking
us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm
Borrowings
Subordinated notes
us-gaap_UnamortizedDebtIssuanceExpense
Unamortized debt issuance costs
Financial Instrument
Remainder of 2024
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear
2026
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
Deposits
Total
2027
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
2028
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
Segment Reporting, Policy [Policy Text Block]
Subsequent Events, Policy [Policy Text Block]
2025
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block]
us-gaap_FiniteLivedIntangibleAssetUsefulLife
Finite-Lived Intangible Asset, Useful Life (Year)
Extended Maturity and Interest Rate Reduction [Member]
INTEREST EXPENSE
Service charges and fee income
us-gaap_InterestAndDividendIncomeOperating
Total interest and dividend income
Commercial And Consumer Banking [Member]
Represent the Commercial and Consumer Banking segment.
Schedule of Finite-Lived Intangible Assets [Table Text Block]
Thereafter
fsbw_FinitelivedIntangibleAssetExpectedAmortizationAfterYearFour
Amount of amortization for asset, excluding financial asset and goodwill, lacking physical substance with finite life expected to be recognized after fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
us-gaap_LesseeOperatingLeaseRenewalTerm
Lessee, Operating Lease, Renewal Term (Year)
The 2018 Equity Incentive Plan [Member]
Represents the the 2018 Equity Incentive Plan.
us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff
Revolving, Writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff
Revolving, Converted to Term Loan, Writeoff
Officers And Employees [Member]
Represents Officers And Employees.
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff
Three Years before Current Fiscal Year, Writeoff
Certificates of deposit of $100,000 through $250,000
us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff
Four Years before Current Fiscal Year, Writeoff
us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Common stock repurchased for employee/director taxes paid on restricted stock awards (in shares)
Home Lending [Member]
Represents the home lending segment.
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff
More than Five Years before Current Fiscal Year, Writeoff
Granted, Intrinsic Value
Represents the intrinsic value of options granted in the period.
Maturing in 2024
us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesPercent
% of total loan type
Mandatory and Best Effort Forward Commitments [Member]
Represents mandatory and best effort forward commitments with investors.
Forward TBA Mortgage-Backed Securities [Member]
Represents forward TBA mortgage-backed securities.
us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff
Two Years before Current Fiscal Year, Writeoff
Share-Based Payment Arrangement, Tranche Four [Member]
Fourth portion of award under share-based payment arrangement differentiated by vesting feature, including, but not limited to, performance measure or service period.
us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff
Current Fiscal Year, Writeoff
fsbw_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExpectedContractualTermForfeitureRate
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expected Contractual Term Forfeiture Rate
Represents the percentage of options estimated to be forfeited over the contractual term.
us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff
Fiscal Year before Current Fiscal Year, Writeoff
us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification
Weighted-average period (Year)
Maturing in 2028
Mortgage Servicing Rights [Member]
Represents Mortgage Servicing Rights.
Maturing in 2025
Deposit Liabilities, Certificates of Deposits [Member]
Represents interest-bearing domestic certificate of deposit liabilities.
Maturing in 2026
Escrow accounts related to mortgages serviced
Amount of the escrow accounts related to mortgages serviced noninterest-bearing deposit liabilities.
Maturing in 2027
Time Deposit Maturities [Table Text Block]
Deposit Liabilities, Money Market [Member]
Represents interest-bearing domestic money market demand account deposit liabilities.
Deposit Liabilities, Checking [Member]
Represents interest-bearing checking deposit liabilities.
Thereafter, operating lease
Amount of lessee's undiscounted obligation for lease payment for operating lease due after fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
Thereafter
Amount of time deposit maturing after fourth fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
Loans receivable, including fees
Real Estate Owned (OREO) [Member]
Represents Real estate owned.
Capital Adequacy, Tier 1 Risk-based with Buffer, Rate
Represents the rate of minimum Tier 1 risk-based capital required with conservation buffer for capital adequacy as defined by regulatory framework.
Capital Adequacy, Total Risk-based with Buffer, Rate
Represents the rate of minimum total risk-based capital required with conservation buffer for capital adequacy as defined by regulatory framework.
Capital Adequacy, CET 1 with Buffer , Rate
Represents the rate of minimum Common Equity Tier 1 risk-based capital required with conservation buffer for capital adequacy as defined by regulatory framework.
Capital Adequacy, Tier 1 Risk-based with Buffer
Represents the amount of minimum Tier 1 risk-based capital required with conservation buffer for capital adequacy as defined by regulatory framework.
Capital Adequacy, Total Risk-based with Buffer
Represents the amount of minimum total risk-based capital required with conservation buffer for capital adequacy as defined by regulatory framework.
Noninterest-bearing checking
Capital Adequacy, CET 1 with Buffer
Represents the amount of minimum Common Equity Tier 1 risk-based capital required with conservation buffer for capital adequacy as defined by regulatory framework.
Industry Sources [Member]
Valuation approach using price and other relevant information generated by the industry.
First Security Bank of Washington, Subsidiary [Member]
Entity in which controlling financial interest is held. Includes, but is not limited to, variable interest entity (VIE) consolidated by primary beneficiary. Excludes entity in which broker-dealer holds controlling financial interest but control is likely to be temporary.
Pull-through Expectations Rate [Member]
Measurement input using pull-through expectations rate.
INTEREST INCOME
Customer Swap [Member]
Represents customer swap contract.
Dealer Offsets to Customer Swap [Member]
Represents the dealer offsets to customer swap.
Brokered Deposits and Borrowings [Member]
Represents brokered deposits and borrowings.
us-gaap_InterestBearingDomesticDepositChecking
Interest-bearing checking
Sensitivity Analysis of Fair Value, Impact of 1.0 Percent Adverse Change in Other Assumption [Member]
Represents the impact of a specified percentage variance in a specified key assumption in the determination of fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities).
us-gaap_NoninterestIncome
Noninterest income
Total noninterest income
us-gaap_InterestBearingDomesticDepositBrokered
Interest-Bearing Domestic Deposit, Brokered
Impairment of MSRs
Certificates of deposit less than $100,000
Sensitivity Analysis of Fair Value, Impact of 0.5 Percent Adverse Change in Other Assumption [Member]
Represents the impact of a specified percentage variance in a specified key assumption in the determination of fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities).
Certificates of deposit greater than $250,000
Other noninterest income
Marine Loans [Member]
Represents marine loans.
Earnings on cash surrender value of BOLI
Deposit Liabilities Disclosures [Text Block]
Warehouse Lending Loan [Member]
Represents warehouse lending loans.
Real Estate Portfolio Segment [Member]
Portfolio segment of the company's total financing receivables related to real estate.
NONINTEREST INCOME
Indirect Home Improvement Loan [Member]
Represents indirect home improvement loans.
One-to-four Family Loan [Member]
Represents one-to-four family loan.
PROVISION FOR CREDIT LOSSES
Provision for credit losses
(Provision) recovery for credit losses
us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss
NET INTEREST INCOME AFTER PROVISION FOR CREDIT LOSSES
Watch [Member]
A category of financing receivables considered to have potential weaknesses that deserve management's close attention. If left uncorrected, those potential weaknesses may result in a deterioration of the repayment prospects for the asset or of the creditor's position at some future date.
us-gaap_InterestIncomeExpenseNet
Net interest income
NET INTEREST INCOME
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Gain on sale of MSRs
Gain on sale of MSRs
Amount of gain (loss) from sale and disposal of mortgage servicing rights.
us-gaap_NumberOfOperatingSegments
Number of Operating Segments
Segment Reporting Disclosure [Text Block]
Interest Income and Interest Expense Disclosure [Table Text Block]
Debit Card [Member]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations
CASH AND CASH EQUIVALENTS, beginning of period
CASH AND CASH EQUIVALENTS, end of period
Assets [Abstract]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS
Interest and dividends on investment securities, cash and cash equivalents, and certificates of deposit at other financial institutions
Less forfeited, Intrinsic Value
Represents the intrinsic value of options forfeited during the period.
us-gaap_NetCashProvidedByUsedInFinancingActivities
Net cash used by financing activities
Director [Member]
us-gaap_NetCashProvidedByUsedInOperatingActivities
Net cash from operating activities
us-gaap_NetCashProvidedByUsedInInvestingActivities
Net cash from investing activities
Base Rate [Member]
us-gaap_BankingRegulationCapitalConservationBufferCapitalConservedMinimum
Banking Regulation, Capital Conservation Buffer, Capital Conserved, Minimum
Capital Adequacy, CET 1 Rate
Well Capitalized, CET 1 Rate
us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation
Common stock repurchased for employee/director taxes paid on restricted stock awards
us-gaap_PaymentsOfDividendsCommonStock
Dividends paid on common stock
us-gaap_NoninterestExpense
Noninterest Expense
Total noninterest expense
Noninterest expense
Issuance of common stock - employee stock purchase plan
Scenario [Domain]
Federal Deposit Insurance Corporation (“FDIC”) insurance
Loan costs
us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Noninterest income (in-scope of Topic 606)
Title and Position [Domain]
Title and Position [Axis]
Scenario [Axis]
NONINTEREST EXPENSE
Residential Real Estate [Member]
Collateral Held [Domain]
Unfunded Loan Commitment [Member]
Collateral Held [Axis]
Class of Financing Receivable [Domain]
Construction Loans [Member]
Home Equity Loan [Member]
Unallocated Financing Receivables [Member]
Commercial Real Estate Portfolio Segment [Member]
Class of Financing Receivable [Axis]
Financing Receivable Portfolio Segment [Domain]
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Income before provision for income taxes
Consumer Portfolio Segment [Member]
Financing Receivable Portfolio Segment [Axis]
us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss
us-gaap_DebtSecuritiesHeldToMaturityAccruedInterestBeforeAllowanceForCreditLoss
Debt Securities, Held-to-Maturity, Accrued Interest, before Allowance for Credit Loss
Disaggregation of Revenue [Table Text Block]
Interest Rate Swap Agreements [Member]
Represents interest rate swap agreement.
Recoveries
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff
Charge-offs
Allowance for Credit Loss, Writeoff
Revenue from Contract with Customer [Text Block]
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecovery
Net charge-offs
us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings
Repayments of borrowings
us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Provision for credit losses on loans
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]
Expected Forfeiture Rate
Represents the share-based compensation arrangement by share-based payment award options expected forfeiture rate.
Dividends paid, per share (in dollars per share)
Proceeds from borrowings
fsbw_FinancingReceivableModifiedSubsequentDefaultNumberOfContracts
Financing Receivable, Modified, Subsequent Default, Number of Contracts
Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
fsbw_LoansServiced
Loans Serviced
Amount of loans serviced as of balance sheet date.
Dilutive shares (in shares)
Pledging Purpose [Domain]
Potentially dilutive weighted average share options that were not included in the computation of diluted earnings per share because to do so would be anti-dilutive. (in shares)
us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Diluted weighted average common shares outstanding (in shares)
Pledging Purpose [Axis]
us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]
us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss
Financing Receivable, Accrued Interest, after Allowance for Credit Loss
Asset Class [Axis]
Asset Class [Domain]
Statement of Financial Position [Abstract]
Diluted earnings per share (in dollars per share)
Basic weighted average common shares outstanding (in shares)
MSRs held for sale, held at the lower of cost or fair value
The amount of mortgage servicing asset held for sale.
us-gaap_FinancingReceivableRevolvingConvertedToTermLoan
Financing Receivable, Revolving, Converted to Term Loan
us-gaap_FinancingReceivableUnamortizedLoanFeeCost
Financing Receivable, Unamortized Loan Cost (Fee)
Business Acquisition [Axis]
Basic earnings per share (in dollars per share)
Business Acquisition, Acquiree [Domain]
Available-for-Sale, Allowance for Credit Loss
Statement of Cash Flows [Abstract]
us-gaap_FinancingReceivableUnamortizedPurchasePremiumDiscount
Financing Receivable, Unamortized Purchase Premium (Discount)
Statement of Stockholders' Equity [Abstract]
us-gaap_LesseeOperatingLeaseRemainingLeaseTerm
Lessee, Operating Lease, Remaining Lease Term (Month)
Financing Receivable, Nonaccrual [Table Text Block]
Investments Classified by Contractual Maturity Date [Table Text Block]
Securities available for sale, HTM, ACL
Securities held-to-maturity, allowance for losses
Beginning ACL balance
Total ending ACL balance
us-gaap_DebtSecuritiesHeldToMaturity90DaysOrMorePastDueStillAccruing
Debt Securities, Held-to-Maturity, 90 Days or More Past Due, Still Accruing
Net decrease in deposits
Financing Receivable, Nonaccrual, With Allowance
Amortized cost of financing receivable on nonaccrual status with allowance for credit loss. Excludes net investment in lease.
Weighted average rate of loans in MSRs portfolio
Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Table Text Block]
Schedule of Realized Gain (Loss) [Table Text Block]
U.S. Small Business Administration Securities [Member]
Represent U.S. Small Business Administration securities.
Financing Receivable, Collateral Dependent Loans [Table Text Block]
Tabular disclosure of collateral dependent financing receivable.
Provision for (recapture of) credit losses
Other Nonreal Estate [Member]
Represents other nonreal estate property.
us-gaap_DebtSecuritiesHeldToMaturityNonaccrual
Debt Securities, Held-to-Maturity, Nonaccrual
Fair Value Measurements, Nonrecurring [Table Text Block]
Federal Reserve Bank, Bank Term Funding Program [Member]
Represents the Bank Term Funding Program of Federal Reserve Bank.
us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Table Text Block]
CASH FLOWS USED BY FINANCING ACTIVITIES
Mortgage Servicing Right, Held for Sale [Member]
Represents MSR, held for sale.
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
us-gaap_BusinessCombinationAcquiredReceivablesGrossContractualAmount
Business Combination, Acquired Receivables, Gross Contractual Amount
us-gaap_BusinessCombinationAcquiredReceivablesEstimatedUncollectible
Business Combination, Acquired Receivables, Estimated Uncollectible
Standard & Poor's, BBB/BBB Minus Rating [Member]
Represents BBB/BBB- credit rating as defined by the external credit rating agency, Standard & Poor's.
us-gaap_BusinessCombinationAcquiredReceivablesFairValue
Business Combination, Acquired Receivable, Fair Value
us-gaap_AssetsAverageOutstanding
Total average assets for period ended
Pledged Status [Domain]
Pledged Status [Axis]
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Total liabilities assumed
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther
Other liabilities
Class of Stock [Axis]
Net cash from acquisitions
Cash Acquired from Acquisition
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
us-gaap_PaymentsToAcquireBusinessesGross
Payments to Acquire Businesses, Gross
Recourse [Member]
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
Total assets acquired
Liabilities
us-gaap_RevenueNotFromContractWithCustomerExcludingInterestIncome
Noninterest income (out-of-scope and/or immaterial to Topic 606)
Amortized cost
us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss
Recourse Status [Domain]
Gross unrealized gains
Recourse Status [Axis]
us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss
Gross unrealized losses
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block]
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
Premises and equipment
Total securities, allowance for credit loss
us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAllowanceForCreditLoss
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets
Other assets
Held to maturity securities, fair value, total
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill
Core deposit intangible ("CDI")
Notional
fsbw_DebtSecuritiesHeldtomaturityUnrealizedLossPositionAccumulatedLoss1
Held-to-maturity, total
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
12 months or longer, unrealized loss, fair value, held to maturity securities
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer.
fsbw_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss1
12 months or longer, unrealized loss, held to maturity securities
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.
fsbw_FinancingReceivableModifiedWeightedAverageInterestRatePostmodification
Post-modification %
Percentage of post-modification weighted average contractual interest rate of financing receivable modified for debtor experiencing financial difficulty.
Hedging Relationship [Domain]
Total securities, fair value
fsbw_FinancingReceivableModifiedWeightedAverageInterestRateOriginalPercentage
Pre-modification %
Percentage of original weighted average contractual interest rate of financing receivable modified for debtor experiencing financial difficulty.
Fair Value Hedging [Member]
Cash Flow Hedging [Member]
Not Designated as Hedging Instrument [Member]
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables
Loans receivable
Hedging Relationship [Axis]
fsbw_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss1
Less than 12 months, held to maturity securities
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.
Hedging Designation [Axis]
Securities held-to-maturity, net of allowance for credit losses of $45 and $45 (fair value of $7,785 and $7,666, respectively)
us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents
Cash and cash equivalents
Hedging Designation [Domain]
Designated as Hedging Instrument [Member]
Less than 12 months, fair value, held to maturity
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months.
Assets
Additions as a result of the Branch Purchase
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
us-gaap_NumberOfBusinessesAcquired
Number of Businesses Acquired
Pass [Member]
Less than 12 months, fair value
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale and held-to-maturity), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
fsbw_DebtSecuritiesAvailableforsaleAndHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Less than 12 months, unrealized loss
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (available-for-sale and held-to-maturity), in continuous loss position for less than 12 months.
Proceeds from sale of investment securities
Proceeds from Sale of Debt Securities, Available-for-Sale
Internal Credit Assessment [Axis]
Maturities, prepayments, and calls
Internal Credit Assessment [Domain]
Nonvested Restricted Stock Shares Activity [Table Text Block]
us-gaap_PaymentsToAcquireRestrictedCertificatesOfDeposit
Purchase of certificates of deposit at other financial institutions
us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt
Purchases
Financial Asset, Past Due [Member]
us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Beginning balance
Total ending ACL balance
Financial Asset, Not Past Due [Member]
Goodwill and Intangible Assets Disclosure [Text Block]
Commercial And Industrial [Member]
Represents commercial and industrial loans.
us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Total financing receivable, gross
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]
Financing Receivable, Nonaccrual, No Allowance
us-gaap_FinancingReceivableNonaccrualInterestIncome
Financing Receivable, Nonaccrual, Interest Income
12 months or longer, fair value
Fair value of investment in debt security measured at amortized cost (available-for-sale and held-to-maturity), in continuous unrealized loss position for 12 months or longer.
us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year
Special Mention [Member]
us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear
Financing Receivable, Year Five
us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear
Financing Receivable, Originated, More than Five Years before Current Fiscal Year
Substandard [Member]
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear
Financing Receivable, Year Four
us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear
Financing Receivable, Year One
Doubtful [Member]
fsbw_ExpectedCreditLossesOnInvestments
Expected Credit Losses on Investments
The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.
fsbw_DebtSecuritiesAvailableforsaleAndHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
12 months or longer, unrealized loss
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (available-for-sale and held-to-maturity), in continuous loss position for 12 months or longer.
us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear
Financing Receivable, Year Three
us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year
us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear
Financing Receivable, Prior
fsbw_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions
Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions
Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (held-to-maturity), in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.
us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year
us-gaap_FinancingReceivableExcludingAccruedInterestRevolving
Financing Receivable, Revolving
fsbw_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions
Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions
Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (held-to-maturity), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.
us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear
Financing Receivable, Year One, Originated, Current Fiscal Year
us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan
Financing Receivable, Converted to Term
Debt Securities, fair value, total
Total fair value of investment in debt security measured at amortized cost (available-for-sale and held-to-maturity), in continuous unrealized loss position.
fsbw_DebtSecuritiesAvailableforsaleAndHeldtomaturityContinuousUnrealizedLossPositionAccumulatedLossTotal
Debt securities, unrealized loss, total
Total amount of accumulated unrealized loss on investment in debt security measured at amortized cost (available-for-sale and held-to-maturity), in continuous loss position.
us-gaap_FinancingReceivableRevolving
Financing Receivable, Revolving
us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear
Financing Receivable, Year Two
us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Purchase of premises and equipment
Loans transferred to OREO
SUPPLEMENTARY DISCLOSURES OF NONCASH OPERATING, INVESTING AND FINANCING ACTIVITIES
State and Local Government Public Deposits [Member]
Represents State and local government public deposits.
us-gaap_FinancingReceivableModificationsRecordedInvestment
Amortized cost basis
Income taxes
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsAccruedInterestReceivables
Accrued interest receivable
Represents accrued interest receivable in a business combination.
SUPPLEMENTARY DISCLOSURES OF CASH FLOW INFORMATION
Investment Securities, Amortized Cost
Represents the amortized cost of financial instruments.
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesNoninterestbearingDeposits
Noninterest-bearing accounts
Amount of noninterest-bearing deposits liabilities assumed at the acquisition date.
Payment Deferral [Member]
Total deposits
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesDepositsTotal
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities, Deposits, Total
Amount of deposit liabilities assumed at the acquisition date.
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesInterestbearingDeposits
Interest-bearing accounts
Amount of interest-bearing deposit liabilities assumed at the acquisition date.
Loan Restructuring Modification [Axis]
Loan Restructuring Modification [Domain]
us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Net income available to common shareholders
Workforce and Customer Relationships [Member]
Represents workforce and customer relationships .
fsbw_NumberOfBusinessesAcquiredLeasesAcquiredWithBankBranches
Number of Businesses Acquired, Leases Acquired with Bank Branches
Represents the number of leases acquired.
Business Combination, Payment for Loans Acquired [Member]
Information pertaining to loans acquired.
Investment [Text Block]
fsbw_NumberOfFinancialAssetsPurchasedWithCreditDeterioration
Number of Financial Assets Purchased with Credit Deterioration
Represents the number of financial assets purchased with credit deterioration.
Investment [Table Text Block]
Reported Value by Acquiree [Member]
Represents the reported value by the acquiree in a business combination.
Financing Receivable, Modified [Table Text Block]
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAccruedInterestPayable
Accrued interest payable
Amount of accrued interest liabilities assumed at the acquisition date.
fsbw_NumberOfBusinessesAcquiredBankOwnedBranches
Number of Businesses Acquired, Bank Owned Branches
The number of businesses acquired by the entity during the period.
Core Deposits [Member]
Fair Value Adjustment [Member]
Represents the fair value adjustments in a business combination.
us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic
Dividends and undistributed earnings allocated to participating securities
Business Combination, Payment for Core Deposits and Deposits Assumed [Member]
Information pertaining to core deposits and deposits assumed.
Business Combination, Payment for Bank Facilities and Other Assets [Member]
Information pertaining to bank facilities and certain other assets associated with the acquired branches.
Finite-Lived Intangible Assets by Major Class [Axis]
fsbw_BusinessCombinationPublicFundsPercentage
Business Combination, Public Funds, Percentage
Represents the percentage paid for public funds in a business combination.
Finite-Lived Intangible Assets, Major Class Name [Domain]
fsbw_BusinessCombinationCoreDepositsPremiumPercentage
Business Combination, Core Deposits Premium, Percentage
Represents the deposit premium for core deposits as a percentage.
us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation
Common stock repurchased for employee/director taxes paid on restricted stock awards
fsbw_EscrowHoldbackRelativeToOutstandingCreditEnhancementCeObligation
Escrow Holdback Relative to Outstanding Credit Enhancement (CE) Obligation
Represents the amount established as an escrow holdback relative to the amount of outstanding credit obligation.
Federal Home Loan Mortgage Corporation (FHLMC) [Member]
fsbw_AmountToOutstandingCreditEnhancementCeObligationPercentage
Amount to Outstanding Credit Enhancement (CE) Obligation, Percentage
Represents the amount established as A Percentage of Outstanding Credit Enhancement (CE) Obligation
Holdback Reserve For Guaranteed Loans [Member]
Represents the holdback reserve established to cover loss exposure related to these guarantees for loans.
fsbw_FirstLossAccountFLA
First Loss Account (FLA)
Represents the establishment of a first loss account (“FLA”) related to loans.
Government National Mortgage Association (GNMA) [Member]
fsbw_CreditEnhancementCEObligationPercentageOfOutstandingLoans
Credit Enhancement (CE) Obligation, Percentage of Outstanding Loans
Represents the credit enhancement (“CE”) obligation as a percentage of the outstanding loans.
fsbw_CreditEnhancementCEObligation
Credit Enhancement (CE) Obligation
Represents the required credit enhancement (“CE”) obligation.
Federal National Mortgage Association (FNMA) [Member]
Loans Insured or Guaranteed by Government Authorities [Axis]
Loans Insured or Guaranteed by Government Authorities [Domain]
Full-time employees ("FTEs")
Number of full-time persons employed by the Entity
Net income
Net income
Net income
us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Financing Receivable, 90 Days or More Past Due, Still Accruing
Financing Receivable Credit Quality Indicators [Table Text Block]
Restricted Stock [Member]
Share-Based Payment Arrangement, Option [Member]
Financing Receivable, Nonaccrual
Financial Asset, 30 to 59 Days Past Due [Member]
Financial Asset, 60 to 89 Days Past Due [Member]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Table Text Block]
Financial Asset, Aging [Axis]
Financial Asset, Aging [Domain]
Financing Receivables [Text Block]
Business Combination Disclosure [Text Block]
Maturities of certificates of deposit at other financial institutions
us-gaap_PaymentsToAcquireLoansHeldForInvestment
Purchase of portfolio loans
us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock
Change in FHLB stock, net
Proceeds from sale of mortgage servicing rights
CASH FLOWS FROM INVESTING ACTIVITIES
Earnings Per Share [Text Block]
us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
Other liabilities
Lessee, Operating Lease, Supplemental Cash Flow Information [Table Text Block]
Tabular disclosure of supplemental information related to operating leases.
us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax
Income tax (provision) benefit related to unrealized derivative gain (loss)
Income tax provision related to reclassification, net
Income tax provision related to reclassification for realized loss, net
us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax
Income tax benefit (provision) related to unrealized holding (loss) gain
us-gaap_AllocatedShareBasedCompensationExpense
Share-Based Payment Arrangement, Expense
us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Financing Receivable, Allowance for Credit Loss, Recovery
us-gaap_ComprehensiveIncomeNetOfTax
COMPREHENSIVE INCOME
us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardForfeitures
Restricted stock awards forfeited
us-gaap_SharesOutstanding
Balance (in shares)
Balance (in shares)
Common Stock, Shares, Outstanding (in shares)
Financing Receivable, Allowance for Credit Loss [Table Text Block]
Preferred Stock, Shares Outstanding (in shares)
us-gaap_IncreaseDecreaseInOtherOperatingAssets
Other assets
us-gaap_LeaseCost
Total lease cost
us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
Beginning balance, derivative asset (liability)
Ending balance, derivative asset (liability)
Weighted average discount rate- operating leases
Operating lease cost
Short-term lease cost
Lease, Cost [Table Text Block]
Purchases and issuances, derivative asset (liability)
us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationSales
Sales and settlements, derivative asset (liability)
ROU assets in exchange for lease liabilities
Weighted average remaining lease term- operating leases (in years) (Year)
Gain (Loss) Included in Earnings, derivative asset (liability)
Gain (Loss) Included in Other Comprehensive Income (Loss), derivative asset (liability)
Interim Period, Costs Not Allocable [Domain]
us-gaap_DividendsCommonStockCash
Dividends paid
Nature of Expense [Axis]
us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet
Accrued interest receivable
us-gaap_IncreaseDecreaseInFinanceReceivables
Increase (Decrease) in Finance Receivables
Share-based compensation
Liability Class [Axis]
Fair Value by Liability Class [Domain]
us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Common stock repurchased - repurchase plan
us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Common stock repurchased - repurchase plan (in shares)
Issuance of common stock-employee stock purchase plan (in shares)
Less exercised, options (in shares)
Stock options exercised, net (in shares)
Issuance of common stock-employee stock purchase plan
us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited
Restricted stock awards forfeited (in shares)
us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale
Origination of loans held for sale
Proceeds from sale of loans held for sale
MSR
Granted, options (in shares)
Less forfeited, options (in shares)
Collaborative Arrangement and Arrangement Other than Collaborative [Domain]
us-gaap_LiabilitiesAndStockholdersEquity
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY
Reported Value Measurement [Member]
Asset Pledged as Collateral [Member]
Changes in operating assets and liabilities
Retained earnings
Accumulated other comprehensive loss, net of tax
Measurement Input, Prepayment Rate [Member]
Measurement Input, Discount Rate [Member]
Total, operating lease
us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity
Total securities
Operating lease right-of-use (“ROU”) assets
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue
Total lease payments, operating lease
us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount
Less imputed interest, operating lease
2027, operating lease
Measurement Input Type [Axis]
2028, operating lease
Measurement Input Type [Domain]
Net Investment in Lease, before Allowance for Credit Loss
Valuation, Market Approach [Member]
2025, operating lease
2026, operating lease
Valuation Approach and Technique [Axis]
Valuation Approach and Technique [Domain]
Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]
Compensation expense related to stock options and restricted stock awards
Remainder of 2024, operating lease
Depreciation, amortization and accretion
MSRs
us-gaap_AssetsFairValueDisclosure
Total assets measured at fair value
us-gaap_MortgagesHeldForSaleFairValueDisclosure
Mortgage loans held for sale, at fair value
us-gaap_FinancialLiabilitiesFairValueDisclosure
Financial liabilities
Loans held for sale, at fair value
Loans receivable, at fair value
us-gaap_CashAndCashEquivalentsFairValueDisclosure
Cash and cash equivalents
Change in fair value on fair value and cash flow hedges
Unrealized Gain (Loss) on Derivatives
Fair Value, Nonrecurring [Member]
Common stock, $.01 par value; 45,000,000 shares authorized; 7,805,795 and 7,800,545 shares issued and outstanding at March 31, 2024 and December 31, 2023, respectively
Liabilities assumed
Adjustments to reconcile net income to net cash from operating activities
Assets acquired
Measurement Frequency [Axis]
Measurement Frequency [Domain]
Fair Value, Recurring [Member]
Common Stock, Shares Authorized (in shares)
Common Stock, Shares, Issued (in shares)
Fair Value Measurements, Recurring and Nonrecurring [Table Text Block]
Certificates of Deposit [Member]
Common Stock, Par Value (in dollars per share)
Acquisitions:
Statistical Measurement [Domain]
Operating cash flows from operating leases
Maximum [Member]
Minimum [Member]
Weighted Average [Member]
Product and Service [Axis]
Product and Service [Domain]
Statistical Measurement [Axis]
Preferred stock, $.01 par value; 5,000,000 shares authorized; none issued or outstanding
Preferred Stock, Shares Issued (in shares)
Interest on deposits and borrowings
Preferred Stock, Shares Authorized (in shares)
Portion at Fair Value Measurement [Member]
Federal Home Loan Bank of San Francisco [Member]
Preferred Stock, Par Value (in dollars per share)
Estimate of Fair Value Measurement [Member]
Federal Home Loan Bank of Des Moines [Member]
Measurement Basis [Axis]
Federal Home Loan Bank Branch [Domain]
Fair Value, Inputs, Level 3 [Member]
Fair Value Hierarchy and NAV [Domain]
Fair Value, Inputs, Level 1 [Member]
Federal Home Loan Bank Branch [Axis]
Fair Value, Inputs, Level 2 [Member]
Fair Value Hierarchy and NAV [Axis]
Standard & Poor's, BB+ Rating [Member]
Credit Rating, Standard & Poor's [Axis]
External Credit Rating, Standard & Poor's [Domain]
Statement [Line Items]
Aggregate portfolio principal balance
Fair Value Disclosure, off-Balance-Sheet Risks, Face Amount, Asset
Additional paid-in capital
AOCI Attributable to Parent [Member]
STOCKHOLDERS’ EQUITY
Schedule of Fair Value, off-Balance-Sheet Risks [Table Text Block]
Loans receivable, at fair value
Loans Receivable, Fair Value Disclosure
Fair Value Disclosures [Text Block]
Fair Value, by Balance Sheet Grouping [Table Text Block]
us-gaap_Liabilities
Total liabilities
COMMITMENTS AND CONTINGENCIES (NOTE 10)
Other liabilities
Other Liabilities
Net gains (losses) on fair value hedging relationships: Interest rate swaps – securities, Recognized on hedged items
Recognized on derivatives designated as hedging instruments
Derivative Liability
Derivative liabilities, fair value
Derivatives liabilities
us-gaap_InterestPayableCurrentAndNoncurrent
Accrued interest payable
Consolidated Entities [Axis]
Consolidated Entities [Domain]
Retained Earnings [Member]
Additional Paid-in Capital [Member]
Common Stock [Member]
Equity Components [Axis]
Equity Component [Domain]
Principal amount
Subordinated notes, excluding unamortized debt issuance costs
Document Quarterly Report
Entity Incorporation, State or Country Code
fsbw_StockIssuedDuringPeriodValueStockOptionsExercisedNet
Stock options exercised, net
Value of stock issued as a result of the exercise of stock options, net.
Fair Value, Assets (Liabilities) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
Tabular disclosure of the fair value measurement of assets (liabilities) using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets (liabilities)) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets (liabilities)) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset (liability).
Document Transition Report
Borrowings
Borrowings
Entity Interactive Data Current
Commercial Business Portfolio Segment [Member]
Portfolio segment of the company's total financing receivables related to commercial business receivables.
Collateral Dependent Loans [Member]
Represents collateral dependent loans.
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAdjustmentsInterestbearingDeposits
Interest-bearing accounts
Amount of adjustment to interest-bearing deposit liabilities assumed at the acquisition date.
Interest Expense [Member]
Security Exchange Name
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAdjustmentsReceivables
Loans receivable
Amount of adjustment in due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.
Other Consumer Loan [Member]
Loan or extension of credit for personal, family, or household use excluding real estate, classified as other.
Title of 12(b) Security
fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAdjustmentsDepositsTotal
Total deposits
Amount of adjustments to deposit liabilities assumed at the acquisition date.
Interest Income [Member]
us-gaap_PrepayableFinancialAssetClosedPortfolioLastOfLayerAmortizedCost
Financial Asset, Closed Portfolio, Portfolio Layer Method, Amortized Cost
us-gaap_DepositsFairValueDisclosure
Deposits
Statement of Income Location, Balance [Axis]
Statement of Income Location, Balance [Domain]
Collaborative Arrangement and Arrangement Other than Collaborative [Axis]
Multifamily [Member]
us-gaap_DerivativeAmountOfHedgedItem
Derivative, Amount of Hedged Item
Derivative Assets, Financial Instruments Collateral
Derivative Assets, Cash Collateral
Segments [Axis]
Segments [Domain]
Derivative Asset, Offset
Interest rate lock commitments with customers
Statement [Table]
Income Statement [Abstract]
Other comprehensive income, net of tax
Other comprehensive income, net of tax
us-gaap_Deposits
Total deposits
Unrealized derivative gain (loss) during period
us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax
Reclassification adjustment for realized gain, net included in net income
Interest-bearing accounts
Noninterest-bearing accounts
us-gaap_TimeDeposits
Total
Offsetting Liabilities [Table Text Block]
Derivative liability, cash collateral
Money market
Deposit Liabilities, Type [Table Text Block]
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax
Reclassification adjustment for realized loss, net included in net income
Savings
Unrealized holding (loss) gain during period
Securities available-for-sale:
us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
Derivative liability, net
Derivative Asset, Net
us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss
Net income recognized on fair value hedges
Interest Rate Lock Commitments [Member]
Commitments to Extend Credit [Member]
Offsetting Assets [Table Text Block]
us-gaap_StockholdersEquity
Total stockholders’ equity
Balance
Balance
us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Gross unrealized losses, available for sale securities
Gross unrealized gains, available for sale securities
Interest Rate Swap [Member]
Derivative financial instruments:
Amortized cost, available for sale securities
Available-for-Sale, Amortized Cost
Due after one year through five years, amortized cost
Due after five years through ten years, amortized cost
Due after ten years, amortized cost