Note 19 - Related Party Transactions (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Rent Expense From Leased Office Space [Member]
Related Party Transaction, Amounts of Transaction	$ 110,000	$ 96,500
Employees, Officers, and Directors [Member] \| Equity Ownership From Loans [Member]
Percentage of Equity Represented by Related Party	3.44%	2.10%
Executive Officers and Directors [Member]
Related Party Deposit Liabilities	$ 21,000,000	$ 19,600,000

Represents the percentage of equity that is represented by a related party.

No definition available.

Name:	sfdl_PercentageOfEquityRepresentedByRelatedParty
Namespace Prefix:	sfdl_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

+ Details

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

- Definition

Amount of transactions with related party during the financial reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-3

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=sfdl_RentExpenseFromLeasedOfficeSpaceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=sfdl_EmployeesOfficersAndDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=sfdl_EquityOwnershipFromLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=sfdl_ExecutiveOfficersAndDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: