Investment Securities (Schedule of Amortized Costs and Fair Value of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available for sale
Available-for-sale securities, investment securities, Fair Value	$ 87,991	$ 67,694
Total investment securities available for sale, Gross Unrealized Gains	1,527	56
Total investment securities available for sale, Gross Unrealized Losses	432	433
Total investment securities available for sale, Amortized Cost	86,896	68,071
US Government Agencies [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	5,497	499
Total investment securities available for sale, Gross Unrealized Gains
Total investment securities available for sale, Gross Unrealized Losses	3	1
Total investment securities available for sale, Amortized Cost	5,500	500
SBA Securities [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	490	531
Total investment securities available for sale, Gross Unrealized Gains
Total investment securities available for sale, Gross Unrealized Losses	19	19
Total investment securities available for sale, Amortized Cost	509	550
State and Political Subdivisions [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	16,544	4,184
Total investment securities available for sale, Gross Unrealized Gains	641	3
Total investment securities available for sale, Gross Unrealized Losses	29	24
Total investment securities available for sale, Amortized Cost	15,932	4,205
Asset-backed Securities [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	11,769	13,167
Total investment securities available for sale, Gross Unrealized Gains	2
Total investment securities available for sale, Gross Unrealized Losses	189	184
Total investment securities available for sale, Amortized Cost	11,956	13,351
Mortgage Backed Securities [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	53,691	49,313
Total investment securities available for sale, Gross Unrealized Gains	884	53
Total investment securities available for sale, Gross Unrealized Losses	192	205
Total investment securities available for sale, Amortized Cost	52,999	49,465
Mortgage Backed Securities [Member] \| FHLMC [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	12,196	10,608
Total investment securities available for sale, Gross Unrealized Gains	238	14
Total investment securities available for sale, Gross Unrealized Losses	60	15
Total investment securities available for sale, Amortized Cost	12,018	10,609
Mortgage Backed Securities [Member] \| FNMA [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	32,325	35,140
Total investment securities available for sale, Gross Unrealized Gains	602	34
Total investment securities available for sale, Gross Unrealized Losses	80	169
Total investment securities available for sale, Amortized Cost	31,803	35,275
Mortgage Backed Securities [Member] \| GNMA [Member]
Available for sale
Available-for-sale securities, investment securities, Fair Value	9,170	3,565
Total investment securities available for sale, Gross Unrealized Gains	44	5
Total investment securities available for sale, Gross Unrealized Losses	52	21
Total investment securities available for sale, Amortized Cost	$ 9,178	$ 3,581

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

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

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AgencySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=sfst_SbaSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: