Loans and Allowance for Loan Losses (Schedule of Composition of Loan Portfolio) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 2,389,047	$ 2,142,867
Total gross loans, net of deferred fees, (Percentage)	100.00%	100.00%
Less-allowance for loan losses	$ (36,075)	$ (44,149)
Total loans, net	2,352,972	2,098,718
Commercial Loan [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 1,494,996	$ 1,387,655
Total gross loans, net of deferred fees, (Percentage)	62.60%	64.80%
Commercial Loan [Member] \| Construction Loans [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 87,892	$ 61,467
Total gross loans, net of deferred fees, (Percentage)	3.70%	2.90%
Commercial Loan [Member] \| Owner Occupied Re [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 470,614	$ 433,320
Total gross loans, net of deferred fees, (Percentage)	19.70%	20.20%
Commercial Loan [Member] \| Non Owner Occupied Re [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 628,521	$ 585,269
Total gross loans, net of deferred fees, (Percentage)	26.30%	27.30%
Commercial Loan [Member] \| Business Loan [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 307,969	$ 307,599
Total gross loans, net of deferred fees, (Percentage)	12.90%	14.40%
Consumer Loan [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 894,051	$ 755,212
Total gross loans, net of deferred fees, (Percentage)	37.40%	35.20%
Consumer Loan [Member] \| Construction Loans [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 57,419	$ 40,525
Total gross loans, net of deferred fees, (Percentage)	2.40%	1.90%
Consumer Loan [Member] \| Real Estate Loan [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 648,276	$ 536,311
Total gross loans, net of deferred fees, (Percentage)	27.10%	25.00%
Consumer Loan [Member] \| Home Equity Loan [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 155,049	$ 156,957
Total gross loans, net of deferred fees, (Percentage)	6.50%	7.30%
Consumer Loan [Member] \| Other Consumer [Member]
Composition of loan portfolio
Total gross loans, net of deferred fees	$ 33,307	$ 21,419
Total gross loans, net of deferred fees, (Percentage)	1.40%	1.00%

Loans and leases receivable net of deferred income percentage.

No definition available.

Name:	sfst_LoansAndLeasesReceivableNetOfDeferredIncomePercentage
Namespace Prefix:	sfst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=122038336&loc=d3e74567-122707

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524

+ Details

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

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- References

No definition available.

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=sfst_OwnerOccupiedReMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=sfst_NonOwnerOccupiedReMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=sfst_BusinessLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=sfst_OtherConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: