Organization and Basis of Presentation (Policies)	6 Months Ended
Organization and Basis of Presentation (Policies)	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”) for interim financial information with the instructions for Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by GAAP for complete annual financial statements. In the opinion of the Company’s management, the accompanying financial statements contain all adjustments (consisting of normal recurring entries) necessary to fairly present such interim results. Interim results are not necessarily indicative of the results of operations which may be expected for a full year or any subsequent period. These financial statements should be read in conjunction with the financial statements and notes thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 (“2019 Form 10-K”). The financial statements include the accounts of Siebert and its wholly-owned subsidiaries and upon consolidation, all intercompany balances and transactions are eliminated. The U.S. dollar is the functional currency of the Company and numbers are rounded for presentation purposes. Significant Accounting Policies The Company’s significant accounting policies are included in “Note 2 – Summary of Significant Accounting Policies” in the Company’s 2019 Form 10-K. The following changes to the Company’s significant accounting policies as of June 30, 2020 are primarily due to the acquisition of StockCross. Other than the updates indicated below and in “Note 2 – New Accounting Standards,” there have been no significant changes to the Company’s significant accounting policies.
Cash and Securities Segregated For Regulatory Purposes	Cash and Securities Segregated For Regulatory Purposes MSCO is subject to Customer Account Rule 15c3-3 of the SEC which requires segregation of funds in a special reserve account for the exclusive benefit of customers. Effective upon the Company’s acquisition of StockCross on January 1, 2020, the requirements and special reserve accounts of MSCO and StockCross were combined. See “Note 14 – Capital Requirements” for additional detail.
Receivables From and Payables To Customers	Receivables From and Payables To Customers Accounts receivable from and payable to customers include amounts due and owed on cash and margin transactions. Securities owned by customers are held as collateral for receivables. Receivables from customers are reported at their outstanding principal balance, adjusted for any allowance for doubtful accounts. An allowance is established when collectability is not reasonably assured. When the receivable from a brokerage client is considered to be impaired, the amount of impairment is generally measured based on the fair value of the securities acting as collateral, which is measured based on current prices from independent sources such as listed market prices or broker-dealer price quotations. Securities beneficially owned by customers, including those that collateralize margin or other similar transactions, are not reflected in the statements of financial condition. No valuation allowance for doubtful accounts was necessary as of June 30, 2020 and December 31, 2019.
Receivables From, Payables To, and Deposits With Broker-Dealers and Clearing Organizations	Receivables From, Payables To, and Deposits With Broker-Dealers and Clearing Organizations Accounts receivable from and payable to broker-dealers and clearing organizations includes amounts due from / to introducing broker-dealers, fail-to-deliver and fail-to-receive items, and amounts receivable for unsettled regular-way transactions. Deposits with broker-dealers and clearing organizations include amounts held on deposit with broker-dealers and clearing organizations and are included in the line item “Deposits with broker-dealers and clearing organizations.” MSCO customer transactions for the six months ended June 30, 2020 were both self-cleared and cleared on a fully disclosed basis through National Financial Services Corp. (“NFS”). MSCO customer transactions for the six months ended June 30, 2019 were cleared on a fully disclosed basis through NFS and StockCross, the former of which was an affiliate. As of January 1, 2020, all clearing and other services provided by StockCross are performed by MSCO. The Company operates on a month to month basis with its broker-dealers and clearing organizations and their fees are offset against the Company's revenues on a monthly basis. As of June 30, 2020, the Company’s cash clearing deposits with NFS were $50,000. As of December 31, 2019, MSCO’s cash clearing deposits with NFS and StockCross were $50,000 and $75,000, respectively. Upon the closing of the Company’s acquisition of StockCross on January 1, 2020, all MSCO deposits with StockCross were eliminated. As of June 30, 2020 and December 31, 2019, MSCO had deposits with and other non-current receivables from multiple broker-dealers and clearing organizations of approximately $3.6 million and $1.9 million, respectively. WP’s customer transactions clear on a fully disclosed basis through two clearing broker-dealers, The Goldman Sachs Group, Inc. (“Goldman Sachs”) and Pershing LLC (“Pershing”). Amounts payable to broker-dealers and clearing organizations are offset against amounts receivables from broker-dealers and clearing organizations. Receivables from these broker-dealers and clearing organizations are subject to clearance agreements and include the net receivable from net monthly revenues as well as cash on deposit. As of both June 30, 2020 and December 31, 2019, WP’s cash clearing deposits with Goldman Sachs and Pershing were approximately $2 million and $1 million, respectively. The Company evaluates receivables from broker-dealers and clearing organizations and other receivables for collectability noting no amount was considered uncollectable as of June 30, 2020 and December 31, 2019. No valuation allowance is recognized for these receivables as the Company does not have a history of losses from these receivables and does not anticipate losses in the future. See “Note 10 – Revenue Recognition” for additional detail on the accounting policies for the revenue related to these receivables.
Securities Borrowed and Securities Loaned	Securities Borrowed and Securities Loaned Securities borrowed are recorded at the amount of cash collateral advanced. Securities borrowed transactions require the Company to deposit cash, letters of credit, or other collateral with the lender. Securities loaned are recorded at the amount of cash collateral received. For securities borrowed and loaned, the Company monitors the market value of the securities and obtains or refunds collateral as necessary.
Securities Owned, at Fair Value	Securities Owned, at Fair Value Securities owned, at fair value represent marketable securities owned by the Company at trade-date valuation. See “Note 6 – Fair Value Measurements” for additional detail.
Payables to Non-Customers	Payables to Non-Customers Accounts payable to non-customers includes amounts due on cash and margin transactions on accounts owned and controlled by principal officers, directors and stockholders of the Company. Payables to non-customers amounts include any amounts received from interest on credit balances. Payables to non-customers also include amounts due on cash transactions owned and controlled by the Company’s proprietary accounts of introducing broker-dealers. Effective upon the Company’s acquisition of StockCross on January 1, 2020, the Company no longer had any proprietary accounts of introducing broker-dealers.
Securities Sold, Not Yet Purchased, at Fair Value	Securities Sold, Not Yet Purchased, at Fair Value Securities sold, not yet purchased, at fair value represent marketable securities sold by the Company prior to purchase at trade-date valuation. See “Note 6 – Fair Value Measurements” for additional detail.