Note 10 - Deposits (Details Textual) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Time Deposits, $250,000 or More	$ 39,199,506	$ 35,556,760

The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more.

No definition available.

Name:	fsbk_TimeDeposits250000OrMore
Namespace Prefix:	fsbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant