Borrowings and Federal Home Loan Bank Advances (Narrative) (Details)		12 Months Ended
Sep. 27, 2023 USD ($)	Dec. 31, 2023 USD ($) Item
Short-term Debt [Line Items]
Uncommitted secured lines of credit		$ 880,000,000
Number of banks \| Item		4
Daily borrowings under our uncommitted secured lines		$ 240,000,000
Compensating balances		0
Federal Home Loan Bank advances		0
Credit Agreement [Member]
Short-term Debt [Line Items]
Credit agreement maturity date	Sep. 27, 2028
Termination of committed revolving credit facility	$ 500,000,000
Committed revolving credit facility with bank and broker dealer - subsidiary	$ 750,000,000
Outstanding credit facility		0
Company Owned Securities [Member]
Short-term Debt [Line Items]
Uncommitted secured lines of credit		$ 0
Federal Home Loan Bank advances [Member]
Short-term Debt [Line Items]
Weighted average interest rate on borrowings		4.99%

Daily borrowings under credit arrangements.

No definition available.

Name:	sf_DailyBorrowingsUnderCreditArrangements
Namespace Prefix:	sf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of credit facility maximum borrowing capacity terminated.

+ References

No definition available.

+ Details

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

- Definition

Number of banks with which entity has committed revolving credit facility.

+ References

No definition available.

+ Details

Name:	sf_NumberOfBanksWithWhichEntityHasCommittedRevolvingCreditFacility
Namespace Prefix:	sf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Uncommitted secured lines of credit.

+ References

No definition available.

+ Details

Name:	sf_UncommittedSecuredLinesOfCredit
Namespace Prefix:	sf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Weighted average interest rate on borrowings.

+ References

No definition available.

+ Details

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Namespace Prefix:	sf_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of a specific compensating balance arrangement that is maintained under an agreement for a bank loan or future credit availability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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

- Definition

Amount of Federal Home Loan Bank (FHLBank) advances to member financial institutions.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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

- Definition

Date the credit facility terminates, in YYYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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Period Type:	duration

- Details

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- Details

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- Details

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Period Type: