XML 53 R42.htm IDEA: XBRL DOCUMENT v3.25.1

Note 2 - Investments - Schedule of Debt Securities, Held-to-Maturity Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Held-to-Maturity, Amortized Cost	$ 10.5	$ 8.5
Standard & Poor's, BBB/BBB Minus Rating [Member]
Debt Securities, Held-to-Maturity, Amortized Cost	$ 10.5	$ 8.5

X

- Definition

Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	srt_CreditRatingStandardPoorsAxis=fsbw_StandardPoorsBBBOrBBBMinusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: