Acquisitions (Schedule of Statements of Financial Condition) (Details) - USD ($)		Jun. 30, 2020	Dec. 31, 2019		Jun. 30, 2019
ASSETS
Cash and cash equivalents		$ 4,179,000	$ 4,670,000	[1]	$ 5,231,000
Cash and securities segregated for regulatory purposes		255,683,000	224,924,000	[1]	$ 185,678,000
Receivables from customers		80,378,000	86,331,000	[1]
Receivables from broker-dealers and clearing organizations		2,738,000	3,524,000	[1]
Other receivables		1,000,000	762,000	[1]
Prepaid expenses and other assets		673,000	970,000	[1]
Securities borrowed		167,252,000	193,529,000	[1]
Securities owned, at fair value		2,374,000	3,018,000	[1]
Total Current assets		514,277,000	517,728,000	[1]
Deposits with broker-dealers and clearing organizations		6,593,000	4,951,000	[1]
Furniture, equipment and leasehold improvements, net		950,000	1,150,000	[1]
Software, net		1,671,000	1,888,000	[1]
Lease right-of-use assets		3,062,000	3,951,000	[1]
Deferred tax assets		5,155,000	5,388,000	[1]
Intangible assets, net		891,000	1,022,000	[1]
Goodwill		1,989,000	1,989,000	[1]
Total Assets		536,687,000	538,067,000	[1]
LIABILITIES AND STOCKHOLDERS' EQUITY
Payables to customers		314,098,000	308,091,000	[1]
Payables to non-customers		7,719,000	8,063,000	[1]
Drafts payable		1,975,000	2,834,000	[1]
Payables to broker-dealers and clearing organizations		3,582,000	523,000	[1]
Accounts payable and accrued liabilities		2,600,000	2,443,000	[1]
Securities loaned		159,447,000	170,443,000	[1]
Securities sold, not yet purchased, at fair value		17,000	116,000	[1]
Interest payable		30,000	10,000	[1]
Notes payable - related party		8,000,000	8,000,000	[1]
Current portion of lease liabilities		1,921,000	2,227,000	[1]
Total Current liabilities		499,428,000	502,750,000	[1]
Lease liabilities, less current portion		1,522,000	2,182,000	[1]
Total Liabilities		500,950,000	504,932,000	[1]
Commitments and Contingencies				[1]
Stockholders' equity
Common stock, $.01 par value	[2]	306,000	304,000	[1]
Additional paid-in capital		21,022,000	19,897,000	[1]
Retained earnings		14,409,000	12,934,000	[1]
Total Stockholders' equity		35,737,000	33,135,000	[1]
Total Liabilities and stockholders' equity		$ 536,687,000	538,067,000	[1]
Sieber [Member]
ASSETS
Cash and cash equivalents			3,082,000
Cash and securities segregated for regulatory purposes			110,000
Receivables from customers
Receivables from broker-dealers and clearing organizations			3,067,000
Receivables from related party			1,000,000
Other receivables			223,000
Prepaid expenses and other assets			624,000
Securities borrowed
Securities owned, at fair value
Total Current assets			8,106,000
Deposits with broker-dealers and clearing organizations			3,186,000
Furniture, equipment and leasehold improvements, net			1,131,000
Software, net			1,888,000
Lease right-of-use assets			2,810,000
Equity method investment in related party			3,360,000
Deferred tax assets			4,981,000
Intangible assets, net			1,022,000
Goodwill			1,989,000
Total Assets			28,473,000
LIABILITIES AND STOCKHOLDERS' EQUITY
Payables to customers
Payables to non-customers
Drafts payable
Payables to broker-dealers and clearing organizations
Payables to related parties			7,000
Accounts payable and accrued liabilities			1,473,000
Securities loaned
Securities sold, not yet purchased, at fair value			88,000
Interest payable			10,000
Notes payable - related party			3,000,000
Current portion of lease liabilities			1,291,000
Total Current liabilities			5,869,000
Lease liabilities, less current portion			1,823,000
Total Liabilities			7,692,000
Commitments and Contingencies
Stockholders' equity
Common stock, $.01 par value			271,000
Additional paid-in capital			7,641,000
Retained earnings			12,869,000
Total Stockholders' equity			20,781,000
Total Liabilities and stockholders' equity			28,473,000
StockCross [Member]
ASSETS
Cash and cash equivalents			1,588,000
Cash and securities segregated for regulatory purposes			224,814,000
Receivables from customers			86,331,000
Receivables from broker-dealers and clearing organizations			1,265,000
Receivables from related party
Other receivables			627,000
Prepaid expenses and other assets			346,000
Securities borrowed			193,529,000
Securities owned, at fair value			3,018,000
Total Current assets			511,518,000
Deposits with broker-dealers and clearing organizations			1,840,000
Furniture, equipment and leasehold improvements, net			19,000
Software, net
Lease right-of-use assets			1,141,000
Equity method investment in related party
Deferred tax assets			407,000
Intangible assets, net
Goodwill
Total Assets			514,925,000
LIABILITIES AND STOCKHOLDERS' EQUITY
Payables to customers			308,091,000
Payables to non-customers			9,151,000
Drafts payable			2,834,000
Payables to broker-dealers and clearing organizations			1,406,000
Payables to related parties
Accounts payable and accrued liabilities			963,000
Securities loaned			170,443,000
Securities sold, not yet purchased, at fair value			28,000
Interest payable
Notes payable - related party			5,000,000
Current portion of lease liabilities			936,000
Total Current liabilities			498,852,000
Lease liabilities, less current portion			359,000
Total Liabilities			499,211,000
Commitments and Contingencies
Stockholders' equity
Common stock, $.01 par value			10,000
Additional paid-in capital			12,436,000
Retained earnings			3,268,000
Total Stockholders' equity			15,714,000
Total Liabilities and stockholders' equity			514,925,000
Pro Forma Adjustments (unaudited) [Member]
ASSETS
Cash and cash equivalents
Cash and securities segregated for regulatory purposes
Receivables from customers
Receivables from broker-dealers and clearing organizations			(808,000)
Receivables from related party			(1,000,000)
Other receivables			(88,000)
Prepaid expenses and other assets
Securities borrowed
Securities owned, at fair value
Total Current assets			(1,896,000)
Deposits with broker-dealers and clearing organizations			(75,000)
Furniture, equipment and leasehold improvements, net
Software, net
Lease right-of-use assets
Equity method investment in related party			(3,360,000)
Deferred tax assets
Intangible assets, net
Goodwill
Total Assets			(5,331,000)
LIABILITIES AND STOCKHOLDERS' EQUITY
Payables to customers
Payables to non-customers			(1,088,000)
Drafts payable
Payables to broker-dealers and clearing organizations			(883,000)
Payables to related parties			(7,000)
Accounts payable and accrued liabilities			7,000
Securities loaned
Securities sold, not yet purchased, at fair value
Interest payable
Notes payable - related party
Current portion of lease liabilities
Total Current liabilities			(1,971,000)
Lease liabilities, less current portion
Total Liabilities			(1,971,000)
Commitments and Contingencies
Stockholders' equity
Common stock, $.01 par value			23,000
Additional paid-in capital			(180,000)
Retained earnings			(3,203,000)
Total Stockholders' equity			(3,360,000)
Total Liabilities and stockholders' equity			(5,331,000)
Total Combined Siebert (unaudited) [Member]
ASSETS
Cash and cash equivalents			4,670,000
Cash and securities segregated for regulatory purposes			224,924,000
Receivables from customers			86,331,000
Receivables from broker-dealers and clearing organizations			3,524,000
Receivables from related party
Other receivables			762,000
Prepaid expenses and other assets			970,000
Securities borrowed			193,529,000
Securities owned, at fair value			3,018,000
Total Current assets			517,728,000
Deposits with broker-dealers and clearing organizations			4,951,000
Furniture, equipment and leasehold improvements, net			1,150,000
Software, net			1,888,000
Lease right-of-use assets			3,951,000
Equity method investment in related party
Deferred tax assets			5,388,000
Intangible assets, net			1,022,000
Goodwill			1,989,000
Total Assets			538,067,000
LIABILITIES AND STOCKHOLDERS' EQUITY
Payables to customers			308,091,000
Payables to non-customers			8,063,000
Drafts payable			2,834,000
Payables to broker-dealers and clearing organizations			523,000
Payables to related parties
Accounts payable and accrued liabilities			2,443,000
Securities loaned			170,443,000
Securities sold, not yet purchased, at fair value			116,000
Interest payable			10,000
Notes payable - related party			8,000,000
Current portion of lease liabilities			2,227,000
Total Current liabilities			502,750,000
Lease liabilities, less current portion			2,182,000
Total Liabilities			504,932,000
Commitments and Contingencies
Stockholders' equity
Common stock, $.01 par value			304,000
Additional paid-in capital			19,897,000
Retained earnings			12,934,000
Total Stockholders' equity			33,135,000
Total Liabilities and stockholders' equity			$ 538,067,000

[1] Statement of financial condition as of December 31, 2019 represents the pro forma combination of Siebert and StockCross balances. See "Note 3 - Acquisitions" for additional detail.

[2] Shares outstanding as of December 31, 2019 represents the combined total of the Company's shares outstanding and the shares issued for the Company's acquisition of StockCross. See "Note 1 - Organization and Basis of Presentation" for additional detail.