Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Investments, Cost [Abstract]
Margin loans extended	$ 359.3		$ 359.3		$ 365.4
Receivables from customers	71.8		71.8		$ 52.1
Unsettled customer transactions

Amount due from customers for fees and charges arising from transactions related to the entity's brokerage activities and operations.

No definition available.

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