The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: 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=84173941&loc=SL6953423-111524

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
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

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

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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://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(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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=84173941&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=82894903&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=84173941&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-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=27010918&loc=d3e74567-122707

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. 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=82891408&loc=d3e4428-111522

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

Bank Loans (Recorded Balances Of Loans and Amount Of Allowance Allocated Based Upon Impairment Method by Portfolio Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	$ 8,701		$ 9,105
Allowance for Loan Losses, Collectively Evaluated for Impairment	71,999		58,361
Allowance for Loan Losses, Total	80,700	$ 73,775	67,466	$ 62,229	$ 54,202	$ 45,163
Recorded Investment in Loans, Individually Evaluated for Impairment	24,247		29,213
Recorded Investment in Loans, Collectively Evaluated for Impairment	8,320,379		6,985,208
Recorded Investment in Loans, Total	8,344,626		7,014,421
Residential Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	24		24
Allowance for Loan Losses, Collectively Evaluated for Impairment	10,469		8,406
Allowance for Loan Losses, Total	10,493	9,328	8,430	7,135	5,569	2,660
Recorded Investment in Loans, Individually Evaluated for Impairment	328		171
Recorded Investment in Loans, Collectively Evaluated for Impairment	2,791,941		2,593,405
Recorded Investment in Loans, Total	2,792,269		2,593,576
Commercial And Industrial [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	8,677		9,059
Allowance for Loan Losses, Collectively Evaluated for Impairment	55,903		45,415
Allowance for Loan Losses, Total	64,580	59,572	54,474	47,152	40,805	35,127
Recorded Investment in Loans, Individually Evaluated for Impairment	23,630		28,856
Recorded Investment in Loans, Collectively Evaluated for Impairment	3,103,805		2,409,082
Recorded Investment in Loans, Total	3,127,435		2,437,938
Securities-Based Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,923		2,088
Allowance for Loan Losses, Total	1,923	1,928	2,088	3,312	3,600	3,094
Recorded Investment in Loans, Collectively Evaluated for Impairment	1,836,450		1,819,206
Recorded Investment in Loans, Total	1,836,450		1,819,206
Commercial Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,762		1,520
Allowance for Loan Losses, Total	1,762	1,672	1,520	1,027	932	1,363
Recorded Investment in Loans, Collectively Evaluated for Impairment	328,814		116,258
Recorded Investment in Loans, Total	328,814		116,258
Home Equity Lines Of Credit [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment			20
Allowance for Loan Losses, Collectively Evaluated for Impairment	229		142
Allowance for Loan Losses, Total	229	229	162	271	283	371
Recorded Investment in Loans, Individually Evaluated for Impairment	231		184
Recorded Investment in Loans, Collectively Evaluated for Impairment	28,887		14,855
Recorded Investment in Loans, Total	29,118		15,039
Construction And Land [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Collectively Evaluated for Impairment	903		100
Allowance for Loan Losses, Total	903	303	100	233	224	232
Recorded Investment in Loans, Collectively Evaluated for Impairment	120,969		7,896
Recorded Investment in Loans, Total	120,969		7,896
Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment			2
Allowance for Loan Losses, Collectively Evaluated for Impairment	11		14
Allowance for Loan Losses, Total	11	13	16	103	105	129
Recorded Investment in Loans, Individually Evaluated for Impairment	58		2
Recorded Investment in Loans, Collectively Evaluated for Impairment	109,513		24,506
Recorded Investment in Loans, Total	109,571		24,508
Qualitative [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for Loan Losses, Collectively Evaluated for Impairment	799		676
Allowance for Loan Losses, Total	$ 799	$ 730	$ 676	$ 2,996	$ 2,684	$ 2,187