Deposits (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022
Deposit Liability [Line Items]
Noninterest-Bearing Domestic Deposit, Brokered	$ 5,000,000.0
Interest-bearing Domestic Deposit, Brokered	6,000,000	$ 6,000,000
Overdrafts reclassified to loans	68,000	98,000
Time deposits, $250,000 or more	$ 49,100,000	$ 30,300,000

Time deposits, $250,000 or more

No definition available.

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Namespace Prefix:	sfdl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-SubTopic 405
-Topic 942
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481047/942-405-50-1

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (1)
-Publisher SEC

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (2)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (4)
-Publisher SEC

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (5)
-Publisher SEC

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph c
-Publisher SEC

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E
-Publisher SEC

+ Details

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

- Definition

Amount of interest-bearing domestic third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of noninterest-bearing domestic third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant