Document And Entity Information
Dividend yield
Due after ten years, fair value
Note To Financial Statement Details Textual
Significant Accounting Policies
Subtotal, amortized cost
Note 2 - Investments
Share-Based Payment Arrangement, Option, Exercise Price Range [Table]
Due within one year, amortized cost
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans
Risk-free interest rate
Subtotal, fair value
Note 4 - Mortgage Servicing Rights
Due within one year, fair value
Note 5 - Derivatives
Due after one year through five years, fair value
Note 6 - Leases
Due after five years through ten years, fair value
Note 7 - Deposits
Collateralized Mortgage-Backed Securities [Member]
Note 8 - Commitments and Contingencies
Note 9 - Fair Value Measurements
Note 10 - Earnings Per Share
Note 11 - Stock-based Compensation
Note 12 - Regulatory Capital
Note 13 - Business Segments
Expected volatility
Note 14 - Goodwill and Other Intangible Assets
Note 2 - Investments - Schedule of Amortized Costs and Fair Values of Securities (Details)
Note 2 - Investments - Schedule of Debt Securities, Held-to-Maturity, Allowance for Credit Loss Roll Forward (Details)
Note 2 - Investments - Schedule of Debt Securities, Held-to-Maturity Credit Quality Indicators (Details)
Commercial Real Estate [Member]
Expected term in years (Year)
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term (Year)
Note 2 - Investments - Schedule of Securities Pledged as Collateral (Details)
Asset-Backed Securities [Member]
Note 2 - Investments - Schedule of Investments in Unrealized Loss Position (Details)
Note 2 - Investments - Schedule of Contractual Maturities (Details)
Note 2 - Investments - Schedule of Gain or Loss of Securities (Details)
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Portfolio Loan Composition (Details)
US States and Political Subdivisions Debt Securities [Member]
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Allowance for Credit Losses by Category (Details)
fsbw_GainLossOnPurchaseOfTaxCredits
Gain on purchase of tax credits
The gains and losses resulting from the purchase of tax credits.
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - - Schedule of Modified Financing Receivables (Details)
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Financing Receivable, Modified, Past Due (Details)
Commercial Loan [Member]
Residential Mortgage [Member]
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Past Due Loans (Details)
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Risk Rated Loan by Category (Details)
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Amortized Cost of Nonaccrual Loans (Details)
Note 3 - Loans Receivable and Allowance for Credit Losses - Loans - Schedule of Collateral Dependent Loans (Details)
Note 4 - Mortgage Servicing Rights - Schedule of Mortgage Servicing Rights (Details)
Granted, Weighted Average Grant Date Fair Value (in dollars per share)
Note 4 - Mortgage Servicing Rights - Valuation Assumptions (Details)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
12 months or longer, unrealized loss, available for sale securities
Less vested, Weighted Average Grant Date Fair Value (in dollars per share)
Note 5 - Derivatives - Schedule of Fair Value Hedges Cumulative-basis Adjustment (Details)
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Available for sale securities, unrealized losses
Note 5 - Derivatives - Schedule of Derivative Instruments (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 - Derivatives - Schedule of Hedging Relationship (Details)
Note 5 - Derivatives - Schedule of Offsetting of Derivative Assets (Details)
Note 5 - Derivatives - Schedule of Offsetting of Derivative Liabilities (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Beginning balance, RSA (in shares)
Ending balance, RSA (in shares)
Note 6 - Leases - Schedule of Lease Cost (Details)
Note 6 - Leases - Schedule of Supplemental Information (Details)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Less than 12 months, unrealized loss, available for sale securities
Note 6 - Leases - Schedule of Maturity for Operating Leases (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 7 - Deposits - Schedule of Deposit Liabilities (Details)
US Government Agencies Debt Securities [Member]
Note 7 - Deposits - Schedule of Maturity (Details)
Granted, RSA (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Less vested, RSA (in shares)
fsbw_UnrealizedGainLossOnPortfolioLoansMeasuredUnderFairValueOption
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 - Deposits - Schedule Interest Expense by Category (Details)
Expected to vest, Weighted Average Remaining Contractual Term (Year)
Note 8 - Commitments and Contingencies - Schedule of Commitments (Details)
Note 9 - Fair Value Measurements - Schedule of Financial Assets and Liabilities on a Recurring Basis (Details)
Note 9 - Fair Value Measurements - Schedule of Financial Assets on a Non-recurring Basis (Details)
Cash Flow and Fair Value Hedging [Member]
Represents cash flow and fair value hedges.
Note 9 - Fair Value Measurements - Schedule of Schedule of Financial Assets and Liabilities on a Recurring and Non-recurring Basis (Details)
Exercisable, Intrinsic Value
Note 9 - Fair Value Measurements - Schedule of Reconciliation of Financial Assets and Liabilities with Unobservable Inputs (Details)
Expected to vest, options (in shares)
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 9 - Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments (Details)
Expected to vest, Weighted Average Exercise Price (in dollars per share)
Note 10 - Earnings Per Share - Schedule of Earnings Per Share (Details)
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
Expected to vest, Intrinsic Value
Note 11 - Stock-based Compensation - Schedule of Valuation Assumptions (Details)
Note 11 - Stock-based Compensation - Schedule of Stock Option Awards (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 - Stock-based Compensation - Schedule of Stock Option Awards (Details) (Parentheticals)
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 - Stock-based Compensation - Schedule of Restricted Stock Awards (Details)
Note 12 - Regulatory Capital - Schedule of Comparison (Details)
Note 13 - Business Segments - Schedule of Segment Financial Results (Details)
Available for sale securities, fair value, total
Less exercised, Intrinsic Value
Note 14 - Goodwill and Other Intangible Assets - Schedule of Changes in Intangible Assets (Details)
Note 14 - Goodwill and Other Intangible Assets - Schedule of Amortization (Details)
Exercisable, options (in shares)
Notes To Financial Statements
Notes To Financial Statements [Abstract]
Outstanding, Weighted Average Remaining Contractual Term (Year)
Outstanding, Intrinsic Value
Less than 12 months, fair value, available for sale securities
12 months or longer, unrealized loss, fair value, available for sale securities
ACL, available for sale and held to maturity securities
fsbw_DebtSecuritiesAvailableforsaleAndHeldtomaturityAllowanceForCreditLossExcludingAccruedInterest
Amount of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) excluding accrued interest.
Weighted-average grant date fair value per option granted (in dollars per share)
Total securities, fair value
Fair value of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) excluding accrued interest.
Financing Receivable, Nonaccrual, With Allowance
Amortized cost excluding accrued interest, of financing receivable on nonaccrual status with allowance for credit loss. Excludes net investment in lease.
Amortized cost, available for sale and held to maturity securities
fsbw_DebtSecuritiesAvailableforsaleAndHeldtomaturityExcludingAccruedInterestAmortizedCostBeforeAllowanceForCreditLoss
Total securities, amortized cost
Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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)
Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block]
Financial Instruments Owned and Pledged as Collateral [Table]
Financial Instrument [Axis]
us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Financing Receivable, Modified, Commitment to Lend
Granted, Weighted Average Exercise Price (in dollars per share)
Less exercised, Weighted Average Exercise Price (in dollars per share)
Without single maturity date, fair value
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)
Share-Based Payment Arrangement, Tranche Three [Member]
LIABILITIES
Vesting [Axis]
Vesting [Domain]
Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Payment Arrangement, Tranche Two [Member]
us-gaap_Assets
TOTAL ASSETS
Segment assets
Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]
Plan Name [Axis]
Plan Name [Domain]
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Share-Based Payment Arrangement, Nonvested Award, 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
Commitments and Contingencies Disclosure [Text Block]
Decline in fair value from 20% adverse change (prepayment + discount rate)
Premises and equipment, net
Goodwill
Goodwill
Decline in fair value from 20% adverse change (prepayment-only)
Decline in fair value from 10% adverse change (prepayment + discount rate)
Decline in fair value from 10% adverse change (prepayment-only)
Derivative Liability, Before Offset
us-gaap_NotesReceivableGross
Financing Receivable, before Allowance for Credit Loss
us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue
Earnings on 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]
us-gaap_AvailableForSaleSecuritiesDebtSecurities
Securities available-for-sale
us-gaap_HeldToMaturitySecurities
Securities held-to-maturity, gross
Recovery (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 (BENEFIT) FOR INCOME TAXES
Provision for income taxes by segment
Weighted average constant prepayment rate
Weighted average life in years (Year)
us-gaap_MortgageLoansInProcessOfForeclosureAmount
Mortgage Loans in Process of Foreclosure, Amount
Effective discount rate
Gain (Loss) on Securities [Table Text Block]
us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Net income recognized on cash flow hedges
Schedule of Gain (Loss) on Securities [Table]
Interest-bearing deposits at other financial institutions
Due after one year through five years, fair value, held to maturity
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
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]
Amendment Flag
City Area Code
Investment Securities, Fair Value
New Accounting Pronouncements, Policy [Policy Text Block]
Gain on sale of loans
Gain on sale of loans
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.
Gain (loss) on sale of investment securities, net
Loss on sale of investment securities, net
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
Tier 1 leverage capital (to average assets)
Actual, Tier 1 Leverage Rate
Capital Adequacy, Tier 1 Leverage Rate
Entity Emerging Growth Company
Well Capitalized, Tier 1 Leverage Rate
Document Type
Investment Securities, Carrying Value
Investment Owned, Cost
us-gaap_SecuritiesReceivedAsCollateral
Securities Received as Collateral
Well Capitalized, Total Capital Rate
Entity Small Business
Entity Shell Company
CET 1 capital (to risk-weighted assets)
Actual, CET 1 Rate
Document Information [Line Items]
Document Information [Table]
Total risk-based capital (to risk-weighted assets)
Actual, Capital, Rate
Capital Adequacy, Total Rate
Entity Filer Category
Tier 1 risk-based capital (to risk-weighted assets)
Actual, Tier 1 Risk-based Rate
Entity Current Reporting Status
Capital Adequacy, Tier 1 Risk-based Rate
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
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, beginning
Balance, MSR, ending
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
us-gaap_FinancingReceivableAllowanceForCreditLosses
Financing Receivable, Allowance for Credit Loss
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
Banking Regulation, Regulatory Capital Requirement, Compliance [Table]
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]
Entity Address, State or Province
ecd_NonRule10b51ArrAdoptedFlag
Non-Rule 10b5-1 Arrangement Adopted [Flag]
Material Terms of Trading Arrangement [Text Block]
Marketable Securities [Table]
Entity Common Stock, Shares Outstanding
Trading Arrangements, by Individual [Table]
Municipal Bonds [Member]
Marketing and advertising
Professional and board fees
Securities Investment [Member]
Trading Symbol
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 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.
us-gaap_GainLossOnSaleOfInvestments
Gain on sale of investment securities
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.
Derivative Instruments, Gain (Loss) [Table Text Block]
Derivative Instruments, Gain (Loss) [Table]
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Certificates of deposit
us-gaap_InterestExpenseBorrowings
Interest expense - borrowings
Derivative liability, offset
Interest-bearing checking
us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm
Borrowings
Subordinated notes
Interest expense - subordinated note
us-gaap_UnamortizedDebtIssuanceExpense
Unamortized debt issuance costs
Financial Instrument
Remainder of 2025
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear
2027
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
Deposits
Total
Interest expense - deposits
2028
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
2029
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
Segment Reporting, Policy [Policy Text Block]
Subsequent Events, Policy [Policy Text Block]
2026
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)
INTEREST EXPENSE
Intangible Asset, Finite-Lived [Table]
Service charges and fee income
us-gaap_InterestAndDividendIncomeOperating
Total interest and dividend income
Total interest income by segment
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.
Financing Receivable, Revolving, Writeoff
Financing Receivable, Revolving, Writeoff
Financing Receivable, Revolving, Converted to Term Loan, Writeoff
Financing Receivable, Revolving, Converted to Term Loan, Writeoff
Officers And Employees [Member]
Represents Officers And Employees.
Financing Receivable, Three Years before Current Fiscal Year, Writeoff
Financing Receivable, Three Years before Current Fiscal Year, Writeoff
Certificates of deposit of $100,000 through $250,000
Financing Receivable, Four Years before Current Fiscal Year, Writeoff
Financing Receivable, Four Years before Current Fiscal Year, Writeoff
Common stock repurchased for employee/director taxes paid on restricted stock awards (in shares)
Financing Receivable, Excluding Accrued Interest, Modified in Period, Amount
Financing Receivable, Excluding Accrued Interest, Modified in Period, Amount
Home Lending [Member]
Represents the home lending segment.
Maturing in 2029 and thereafter
Amount of time deposit maturing in fifth fiscal year and thereafter 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).
Granted, Intrinsic Value
Represents the intrinsic value of options granted in the period.
Financing Receivable, More than Five Years before Current Fiscal Year, Writeoff
Financing Receivable, More than Five Years before Current Fiscal Year, Writeoff
Mandatory and Best Effort Forward Commitments [Member]
Represents mandatory and best effort forward commitments with investors.
Financing Receivable, Modified, Past Due [Table]
Forward TBA Mortgage-Backed Securities [Member]
Represents forward TBA mortgage-backed securities.
Financing Receivable, Two Years before Current Fiscal Year, Writeoff
Financing Receivable, Two Years before Current Fiscal Year, Writeoff
Financing Receivable, Current Fiscal Year, Writeoff
Financing Receivable, Current Fiscal Year, Writeoff
Financing Receivable, Excluding Accrued Interest, Modified in Period, to Total Financing Receivables, Percentage
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.
Financing Receivable, Fiscal Year before Current Fiscal Year, Writeoff
Financing Receivable, Fiscal Year before Current Fiscal Year, Writeoff
Maturing in 2028
Mortgage Servicing Rights [Member]
Represents Mortgage Servicing Rights.
Financing Receivable, Modified, Past Due [Table Text Block]
Maturing in 2025
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.
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).
Loans receivable, including fees
Interest income - 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.
The 1st 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.
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
us-gaap_NoninterestIncome
Total noninterest income
Total noninterest income by segment
us-gaap_InterestBearingDomesticDepositBrokered
Interest-Bearing Domestic Deposit, Brokered
(Recovery) impairment of MSRs
Certificates of deposit less than $100,000
Certificates of deposit greater than $250,000
Other noninterest income
Earnings on cash surrender value of BOLI
Marine Loans [Member]
Represents marine loans.
Deposit Liabilities Disclosures [Text Block]
Deposit Liability [Table]
Warehouse Lending Loan [Member]
Represents warehouse lending loans.
fsbw_IntersegmentIncome
Intersegment income
The amount of intersegment income.
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
us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss
NET INTEREST INCOME AFTER PROVISION FOR CREDIT LOSSES
fsbw_SegmentIncome
Total income by segment
The amount of total segment income.
fsbw_InterestExpenseIntersegment
Interest expense - intersegment
The amount of intersegment interest expense.
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.
Financing Receivable, Excluding Accrued Interest, Modified, Weighted Average Term Extension Payment Delay (Year)
Period of increase in weighted average maturity of financing receivable modified (excluding accrued interest) for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days
us-gaap_InterestIncomeExpenseNet
NET INTEREST INCOME
Extended Maturity and Payment Delay [Member]
Loan modification for extension of term of loan in which it must be paid, and the payment delay attributed to the loan.
us-gaap_OtherIncome
Other income
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Schedule of Segment Reporting Information, by Segment [Table]
Gain on sale of MSRs
Gain on sale of MSRs
Gain on sale of MSRs
Amount of gain (loss) from sale and disposal of mortgage servicing rights.
us-gaap_NumberOfReportableSegments
Number of Reportable Segments
Segment Reporting Disclosure [Text Block]
Interest Income and Interest Expense Disclosure [Table Text Block]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations
CASH AND CASH EQUIVALENTS, beginning of period
CASH AND CASH EQUIVALENTS, end of period
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS
Interest and dividends on investment securities, cash and cash equivalents, and certificates of deposit at other financial institutions
Interest income - other interest earnings assets
us-gaap_NetCashProvidedByUsedInFinancingActivities
Net cash from (used by) financing activities
Director [Member]
us-gaap_NetCashProvidedByUsedInOperatingActivities
Net cash from operating activities
us-gaap_NetCashProvidedByUsedInInvestingActivities
Net cash used by investing activities
Total securities held-to-maturity, amortized cost
Fair Value Hedging And Cash Flow Hedging [Member]
Represents information pertaining to the fair value hedging and cash flow hedging.
us-gaap_BankingRegulationCapitalConservationBufferCapitalConservedMinimum
Banking Regulation, Capital Conservation Buffer, Capital Conserved, Minimum
Capital Adequacy, CET 1 Rate
Due after five years through ten years, amortized cost, held to maturity
Due after one year through five years, amortized cost, held to maturity
Well Capitalized, CET 1 Rate
Federal Reserve Bank [Member]
Represents Federal Reserve Bank.
us-gaap_CostOfGoodsAndServicesSoldOverhead
Overhead allocation
us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation
Common stock repurchased for employee/director taxes paid on restricted stock awards
Provision for credit losses
us-gaap_PaymentsOfDividendsCommonStock
Dividends paid on common stock
us-gaap_NoninterestExpense
Noninterest Expense
Total noninterest expense
fsbw_PaymentsToAcquireTaxCredits
Purchase of tax credits
The cash outflow associated with the acquisition of tax credits.
us-gaap_PaymentsForRepurchaseOfCommonStock
Common stock repurchased
Issuance of common stock - employee stock purchase plan
us-gaap_ProceedsFromStockPlans
Federal Deposit Insurance Corporation (“FDIC”) insurance
Loan costs
Title and Position [Domain]
Deposit Liabilities, Certificates of Deposits Less Than 100,000 [Member]
Relating to deposit liabilities from certificates of deposits less than $100,000.
Title and Position [Axis]
NONINTEREST EXPENSE
Residential Real Estate [Member]
Collateral Held [Domain]
Unfunded Loan Commitment [Member]
Collateral Held [Axis]
Class of Financing Receivable [Domain]
Home Equity Loan [Member]
Commercial Real Estate Portfolio Segment [Member]
Class of Financing Receivable [Axis]
Financing Receivable Portfolio Segment [Domain]
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
INCOME BEFORE PROVISION (BENEFIT) FOR INCOME TAXES
Income before provision for income taxes by segment
Residential Portfolio Segment [Member]
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
Interest Rate Swap Agreements [Member]
Represents interest rate swap agreement.
Recoveries
Fair Value of Underlying Collateral [Member]
Represents Fair Value of Underlying Collateral.
Allowance for Credit Loss, Writeoff
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff
Charge-offs
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecovery
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff (Recovery)
Net (charge-offs) recoveries
us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings
Repayments of borrowings
us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Provision for (reversal of) credit losses on loans
Financing Receivable, Nonaccrual
Financing Receivable, Nonaccrual, No Allowance
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)
Receivable Type [Axis]
Receivable [Domain]
Proceeds from borrowings
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
Accounts and Financing Receivables [Table]
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]
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)
us-gaap_FinancingReceivableUnamortizedLoanFeeCost
Financing Receivable, Unamortized Loan Cost (Fee)
Business Combination [Axis]
Basic earnings per share (in dollars per share)
Business Combination [Domain]
Statement of Cash Flows [Abstract]
Statement of Stockholders' Equity [Abstract]
us-gaap_LesseeOperatingLeaseRemainingLeaseTerm
Lessee, Operating Lease, Remaining Lease Term (Year)
Financing Receivable, Nonaccrual [Table Text Block]
Investments Classified by Contractual Maturity Date [Table Text Block]
Net increase (decrease) in deposits
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]
Financing Receivable, Collateral Dependent Loans [Table Text Block]
Tabular disclosure of collateral dependent financing receivable.
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]
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 FROM (USED BY) FINANCING ACTIVITIES
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
Standard & Poor's, BBB/BBB Minus Rating [Member]
Represents BBB/BBB- credit rating as defined by the external credit rating agency, Standard & Poor's.
Proceeds from bank owned life insurance death benefits
SBA USDA Guaranteed Certificates [Member]
Represents SBA/USA guaranteed certificates.
Custom Construction [Member]
Represents custom construction.
Pledged Status [Domain]
Pledged Status [Axis]
Owner Occupied [Member]
Represents owner occupied real estate.
Non-owner Occupied [Member]
Represents non-owner occupied real estate.
Available-for-Sale, Allowance for Credit Loss
Class of Stock [Axis]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Amortized cost, available for sale securities
Available-for-Sale, Amortized Cost
Recourse [Member]
Recourse Status [Domain]
Gross unrealized gains, available for sale and held to maturity securities
Recourse Status [Axis]
us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss
Gross unrealized losses, available for sale and held to maturity securities
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block]
Held to maturity securities, fair value
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
fsbw_DebtSecuritiesHeldtomaturityUnrealizedLossPositionAccumulatedLoss1
Held-to-maturity, unrealized losses
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
Notional
Securities held-to-maturity, ACL
Held-to-Maturity, Allowance for Credit Loss
Beginning ACL balance
Total ending ACL balance
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.
Hedging Relationship [Domain]
Fair Value Hedging [Member]
Securities available-for-sale, at fair value (amortized cost of $335,152 and $310,272, net of allowance for credit losses of $0 and $0, respectively)
Total securities available-for-sale, fair value
Not Designated as Hedging Instrument [Member]
Securities held-to-maturity, at amortized cost (fair value of $32,142 and $8,144, net of allowance for credit losses of $220 and $45, respectively)
Hedging Relationship [Axis]
Derivative Instruments and Hedging Activities Disclosures [Table]
fsbw_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss1
Less than 12 months, 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 less than 12 months.
Hedging Designation [Axis]
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.
Amortized cost, held to maturity securities
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss
Debt Securities, Held-to-Maturity, Amortized Cost
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
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.
Maturities, prepayments, and calls
us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities
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
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
us-gaap_PaymentsToAcquireHeldToMaturitySecurities
Purchases
Financial Asset, Past Due [Member]
us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Financing Receivable, Allowance for Credit Loss
ACL on loans
Beginning balance
Ending balance
Financial Asset, Not Past Due [Member]
Goodwill and Intangible Assets Disclosure [Text Block]
Commercial And Industrial [Member]
Represents commercial and industrial loans.
Loans receivable, net of allowance for credit losses of $30,056 and $31,870 (includes loans of $12,571 and $12,728, at fair value, respectively)
Total loans receivable, net
Financing Receivable, Gross
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss
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_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear
Financing Receivable, Year Five Originated, Fiscal Year before Current Fiscal Year
Special Mention [Member]
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear
Financing Receivable, Year Four, Originated, Fiscal Year before Current Fiscal Year
Substandard [Member]
Financing Receivable, Nonaccrual [Table]
Financing Receivable, Year One, Originated, Current Fiscal Year
Financing Receivable, Year One, Originated, Current Fiscal Year
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.
Financing Receivable, Year Three, Originated, Fiscal Year before Current Fiscal Year
Financing Receivable, Year Three, Originated, Fiscal Year before Current Fiscal Year
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear
Financing Receivable, Prior, Originated, Fiscal Year before Current Fiscal Year
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_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_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan
Financing Receivable, Revolving loans 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 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.
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year
us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Purchase of premises and equipment
SUPPLEMENTARY DISCLOSURES OF NONCASH OPERATING, INVESTING AND FINANCING ACTIVITIES
State and Local Government Public Deposits [Member]
Represents State and local government public deposits.
Income taxes
us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Financing Receivable, Modified, Subsequent Default
SUPPLEMENTARY DISCLOSURES OF CASH FLOW INFORMATION
Investment Securities, Amortized Cost
Represents the amortized cost of financial instruments.
Loan Restructuring Modification [Axis]
Loan Restructuring Modification [Domain]
us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Net income available to common shareholders
Extended Maturity [Member]
Investment [Text Block]
Investment [Table Text Block]
Financing Receivable, Modified [Table Text Block]
Core Deposits [Member]
Financing Receivable, Modified [Table]
us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic
Dividends and undistributed earnings allocated to participating securities
Finite-Lived Intangible Assets by Major Class [Axis]
Finite-Lived Intangible Assets, Major Class Name [Domain]
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
Escrow Holdback Relative 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]
fsbw_NumberOfFulltimeEmployeesFTEs
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]
Financing Receivable, Credit Quality Indicator [Table]
Restricted Stock [Member]
Share-Based Payment Arrangement, Option [Member]
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]
Financing Receivable, Past Due [Table]
Financial Asset, Aging [Axis]
Financial Asset, Aging [Domain]
Financing Receivables [Text Block]
Participating Mortgage Loans [Table]
fsbw_PolicyTable
Maturities of certificates of deposit at other financial institutions
us-gaap_PaymentsToAcquireLoansHeldForInvestment
Purchase of portfolio loans
Proceeds from sale of portfolio loans
Earnings Per Share, Diluted, by Common Class, Including Two-Class Method [Table]
us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock
Change in FHLB stock, net
Proceeds from sale of MSRs
Commercial and Speculative Construction and Development [Member]
Represents the Commercial and speculative construction and development.
CASH FLOWS USED BY INVESTING ACTIVITIES
Residential Custom Construction [Member]
Represents the Residential custom construction.
Earnings Per Share [Text Block]
Individual Forward Sale Commitments With Investors [Member]
Represents the Individual forward sale commitments with investors.
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 (loss) gain
Income tax provision related to reclassification, net
Income tax provision (benefit) related to reclassification for realized loss, net
us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax
Income tax provision related to unrealized gain
Total amounts presented on the Consolidated Statements of Income
Total interest expense
Total interest expense by segment
us-gaap_AllocatedShareBasedCompensationExpense
Share-Based Payment Arrangement, Expense
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)
Preferred Stock, Shares Outstanding (in shares)
Financing Receivable, Allowance for Credit Loss [Table Text Block]
Financing Receivable, Allowance for Credit Loss [Table]
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)
Federal Reserve Bank of San Francisco [Member]
Related to Federal Reserve Bank of San Francisco.
Interim Period, Costs Not Allocable [Domain]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
us-gaap_DividendsCommonStockCash
Dividends paid
fsbw_ServicingAssetHeldAtLowerOfCostOrFairValue
MSRs, held at lower of cost or fair value
The amount of servicing asset held at lower of cost or fair value.
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]
Subordinated notes:
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)
Stock options exercised, net (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)
Restricted stock awards (in shares)
us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale
Origination of loans held for sale
Restricted stock awards
Proceeds from sale of loans held for sale
Proceeds from Sale, Loan, Held-for-Sale
Collateral dependent loans
us-gaap_ServicingAssetMeasurementInput
Granted, options (in shares)
us-gaap_SegmentReportingOtherItemAmount
Other segment items
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
Operating lease liabilities
Operating lease right-of-use (“ROU”) assets
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue
Total lease payments, operating lease
fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentAdverseChangeInDiscountRatePercent
Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Discount Rate, Percent
A 10% percentage variance in the discount rate assumption in the determination of fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities).
us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount
Less imputed interest, operating lease
Measurement Input Type [Axis]
2028, operating lease
Measurement Input Type [Domain]
2029, operating lease
fsbw_FinancingReceivableExcludingAccruedInterestIncreasedecreaseInProvisions
Financing Receivable, Excluding Accrued Interest, Increase/Decrease in Provisions
The increase or decrease in provisions for financing receivables excluding accrued interest.
Valuation, Market Approach [Member]
2026, operating lease
2027, operating lease
Valuation Approach and Technique [Axis]
fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentAdverseChangeInPrepaymentSpeedPercent
Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Prepayment Speed, Percent
A 20% percentage variance in the prepayment speed assumption in the determination of fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities).
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 2025, operating lease
Depreciation, amortization and accretion
Collateral dependent loans
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; 7,535,330 and 7,833,014 shares issued and outstanding at September 30, 2025 and December 31, 2024, respectively
Fair Value, Recurring and Nonrecurring [Table]
Measurement Frequency [Axis]
Adjustments to reconcile net income to net cash from operating activities
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)
Lessee, Lease, Description [Table]
Statistical Measurement [Domain]
Operating cash flows from operating leases
Maximum [Member]
Minimum [Member]
Weighted Average [Member]
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]
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, AA 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, by Balance Sheet Grouping [Table]
Fair Value Disclosures [Text Block]
Fair Value, by Balance Sheet Grouping [Table Text Block]
us-gaap_Liabilities
Total liabilities
COMMITMENTS AND CONTINGENCIES (NOTE 8)
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
Consolidation Items [Domain]
Derivative Liability
Derivative liabilities
Derivatives liabilities
Consolidation Items [Axis]
Parent Company [Member]
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
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.
Interest Expense [Member]
Security Exchange Name
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
Interest Income [Member]
Statement of Income Location, Balance [Axis]
Statement of Income Location, Balance [Domain]
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
us-gaap_DerivativeAssetLiabilityNetMeasurementInput
Statement [Table]
Income Statement [Abstract]
Other comprehensive loss, net of tax
Other comprehensive income (loss), 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
Accounting Standards Update and Change in Accounting Principle [Table]
us-gaap_TimeDeposits
Total
Time deposits
Offsetting Liabilities [Table Text Block]
Derivative liability, cash collateral
Money market
Deposit Liabilities, Type [Table Text Block]
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax
Reclassification adjustment for realized (gain) loss, net included in net income
Savings
Other Commitments [Table]
Unrealized gain during period
Securities available-for-sale:
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]
Operating Segments [Member]
Derivative financial instruments:
Due after one year through five years, amortized cost
Due after five years through ten years, amortized cost
Due after ten years, amortized cost