XML 80 R69.htm IDEA: XBRL DOCUMENT
v3.25.3

Note 7 - Deposits (Details Textual) - USD ($) | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Deposit Liabilities, Money Market [Member] |  |
Interest-Bearing Domestic Deposit, Brokered | $ 251,000 | $ 279,000
Deposit Liabilities, Certificates of Deposits Less Than 100,000 [Member] |  |
Interest-Bearing Domestic Deposit, Brokered | $ 369,400,000 | $ 143,100,000

X
- Definition Amount of interest-bearing domestic third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 + Details
Name: | us-gaap_InterestBearingDomesticDepositBrokered
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=fsbw_DepositLiabilitiesMoneyMarketMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=fsbw_DepositLiabilitiesCertificatesOfDepositsLessThan100000Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |