Loans and Allowance for Loan Losses (Details 9) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Balance, beginning of period	$ 14,855	$ 13,629	$ 11,752
Provision for loan losses	2,000	2,300	3,200
Total loan charge-offs	(1,638)	(1,648)	(1,508)
Loan recoveries	306	574	185
Net loan charge-offs	(1,332)	(1,074)	(1,323)
Balance, end of period	15,523	14,855	13,629
Commercial [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Balance, beginning of period	10,039	9,672
Total loan charge-offs	(1,227)	(1,178)	(1,237)
Loan recoveries	205	558	139
Balance, end of period	9,937	10,039	9,672
Commercial [Member] \| Owner occupied RE [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs		(5)	(48)
Loan recoveries
Commercial [Member] \| Non-owner occupied RE [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs	(589)	(100)	(258)
Loan recoveries	119	155	10
Commercial [Member] \| Business [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs	(638)	(1,031)	(881)
Loan recoveries	86	403	129
Commercial [Member] \| Construction [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs		(42)	(50)
Loan recoveries
Consumer [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Balance, beginning of period	4,816	3,957
Total loan charge-offs	(411)	(470)	(271)
Loan recoveries	101	16	46
Balance, end of period	5,586	4,816	3,957
Consumer [Member] \| Other [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs	(11)	(210)	(5)
Loan recoveries	2	5
Consumer [Member] \| Real estate [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs		(194)	(173)
Loan recoveries	86	10
Consumer [Member] \| Home equity [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs	(400)	(66)	(93)
Loan recoveries	13	1	46
Consumer [Member] \| Construction [Member]
Financing Receivable, Allowance For Credit Losses [Roll Forward]
Total loan charge-offs
Loan recoveries

Allowance for loan and lease losses write offs net of recoveries.

No definition available.

Name:	sfst_AllowanceForLoanAndLeaseLossesWriteOffsNetOfRecoveries
Namespace Prefix:	sfst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

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

- Definition

Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from recoveries of amounts previously written off or reestablishment of reserves that had previously been utilized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialLoanMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
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_LongtermDebtTypeAxis=sfst_OtherConsumerMember
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: