Fair Value Of Financial Instruments (Schedule Of Fair Value Of Investments In And Unfunded Commitments To Funds Measured At Net Asset Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Fair value of investments	$ 43,285	$ 90,809
Unfunded commitments	3,204	12,368
Private Company Investments [Member]
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Fair value of investments		18,763
Unfunded commitments		8,526
Partnership Interests [Member]
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Fair value of investments	5,806	15,798
Unfunded commitments	1,348	1,822
Mutual Funds [Member]
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Fair value of investments	12,441	11,301
Private Equity Funds [Member]
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Fair value of investments	8,673	9,310
Unfunded commitments	1,856	2,020
Money Market Funds [Member]
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Fair value of investments	$ 16,365	$ 35,637

Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

+ Details

Name:	us-gaap_AlternativeInvestmentsFairValueDisclosure
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

No definition available.

+ Details

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

- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

+ Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=sf_PrivateCompanyInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_PartnershipInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MutualFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: