XML 49 R38.htm IDEA: XBRL DOCUMENT
v3.25.3

Note 1 - Basis of Presentation and Summary of Significant Accounting Policies (Details Textual) | Sep. 30, 2025
--- | ---
Number of Bank Branches | 27

X
- Definition Represents the number bank branches. + References No definition available. + Details
Name: | fsbw_NumberOfBankBranches
Namespace Prefix: | fsbw_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant