Investment Securities (Details Textual) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) Investment	Dec. 31, 2017 USD ($) Investment
Investment Securities (Textual)
Sale of investment securities	$ 5,800
loss on sale of investment securities	$ 1
Fair market value, less than 12 months, number of investments \| Investment	29	25
Fair market value, less than 12 months	$ 30,100
Fair market value, 12 months or longer, number of investments \| Investment	27	28
Fair market value,12 months or longer	$ 24,900
Securities pledged as collateral for repurchase agreements from brokers	$ 4,100	$ 7,700

Investment securities.

No definition available.

Name:	sfst_InvestmentSecuritiesTextualAbstract
Namespace Prefix:	sfst_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Investments with fair market value in continuous unrealized loss position for less than twelve months.

+ References

No definition available.

+ Details

Name:	sfst_InvestmentsWithFairMarketValueInContinuousUnrealizedLossPositionLessThanTwelveMonths
Namespace Prefix:	sfst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Investments with fair market value In continuous unrealized loss position twelve months or longer.

+ References

No definition available.

+ Details

Name:	sfst_InvestmentsWithFairMarketValueInContinuousUnrealizedLossPositionTwelveMonthsOrLonger
Namespace Prefix:	sfst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Number of investments in continuous unrealized loss position twelve months or longer.

+ References

No definition available.

+ Details

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

- Definition

The fair value of available-for-sale securities that serve as collateral for borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

+ Details

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

- Definition

The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale.

+ References

No definition available.

+ Details

Name:	us-gaap_GainOnSaleOfInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the sale of debt securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration