Investment Securities (Details)	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Fair market value, less than 12 months, number of investments	115

Number of investments in continuous unrealized loss position, less than twelve months.

No definition available.

Name:	sfst_NumberOfInvestmentsInContinuousUnrealizedLossPositionLessThanTwelveMonths
Namespace Prefix:	sfst_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant