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Financial Instruments with Off-Balance Sheet Risk (Narrative) (Details) $ in Millions | Sep. 30, 2021 USD ($)
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Financial Instruments With Off-balance-sheet Risk And Concentrations Of Credit Risk |
Margin loans extended | $ 1,200.0
Receivables from customers | $ 85.4

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

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- Definition Margin loans extended. + References No definition available. + Details
Name: | SIEB_MarginLoansExtended
Namespace Prefix: | SIEB_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount due from customers for fees and charges arising from transactions related to the entity's brokerage activities and operations. + References No definition available. + Details
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Namespace Prefix: | SIEB_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant