Name:	fsbc_InterestBearingDomesticDepositTimeDeposits250000OrMore
Namespace Prefix:	fsbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of interest-bearing domestic checking deposit liabilities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Name:	us-gaap_InterestBearingDomesticDepositChecking
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of interest-bearing domestic money market demand account deposit liabilities.

Name:	us-gaap_InterestBearingDomesticDepositMoneyMarket
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of interest-bearing domestic deposit liabilities classified as other. Excludes certificates of deposit.

Name:	us-gaap_InterestBearingDomesticDepositOtherTimeDeposit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of interest-bearing domestic savings deposit liabilities. Saving deposits bear interest and have no stated maturity.