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Fair Value Of Financial Instruments (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($)
Fair Value Disclosures [Abstract] |
Transfers of financial assets from Level 2 to Level 1 | $ 0.9
Transfers of financial assets from Level 1 to Level 2 | 0.8
Transfers of financial assets into Level 3 | $ 0.0

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- Definition Fair value level 1 to level 2 transfers amount + References No definition available. + Details
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Namespace Prefix: | sf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Fair Value Level 2 To Level 1 Transfers Amount. + References No definition available. + Details
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Namespace Prefix: | sf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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