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Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024 | Dec. 31, 2024
Financial Instruments with Off-Balance Sheet Risk [Abstract] |  |  |
Margin loans extended | $ 390.1 |  | $ 403.8
Receivables from customers | 79.6 |  | $ 84.4
Unsettled customer transactions |  |  |

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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: | duration

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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
Name: | sieb_ReceivablesFromCustomers1
Namespace Prefix: | sieb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Unsettled customer transactions. + References No definition available. + Details
Name: | sieb_UnsettledCustomerTransactions
Namespace Prefix: | sieb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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