Revenue Recognition (Schedule of Major Revenue Categories) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Trading Execution and Clearing Services
Commissions and fees	$ 20,179,000	$ 9,750,000	[1]
Principal transactions	11,850,000	9,018,000	[1]
Market making	2,042,000	1,744,000
Stock borrow / stock loan	4,045,000	1,607,000
Advisory fees	1,142,000	801,000
Total Trading Execution and Clearing Services	39,258,000	22,920,000
Margin interest, marketing and distribution fees
Margin interest	8,725,000	11,502,000
12b1 fees	1,458,000	3,208,000
Total Margin interest, marketing and distribution fees	10,183,000	14,710,000	[1]
Interest income	4,012,000	4,235,000
Other income	1,419,000	912,000	[1]
Total Other Income	15,614,000	19,857,000
Total Revenue	$ 54,872,000	$ 42,777,000	[1]

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