Revenue Recognition (Schedule of Major Revenue Categories) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Trading Execution and Clearing Services
Commissions and fees	$ 1,750,000	$ 4,019,000	$ 5,943,000	$ 15,352,000
Principal transactions and proprietary trading	953,000	3,924,000	1,767,000	12,279,000
Market making	723,000	1,514,000	2,022,000	4,886,000
Stock borrow / stock loan	4,183,000	3,465,000	11,909,000	7,552,000
Advisory fees	437,000	441,000	1,420,000	1,200,000
Total Trading Execution and Clearing Services	8,046,000	13,363,000	23,061,000	41,269,000
Other Income
Interest	1,387,000	1,014,000	2,195,000	3,331,000
Margin interest	3,169,000	2,251,000	7,336,000	6,698,000
12b-1 fees	648,000	170,000	1,186,000	488,000
Total Interest, marketing and distribution fees	5,204,000	3,435,000	10,717,000	10,517,000
Other income	1,086,000	253,000	2,589,000	982,000
Total Revenue	$ 14,336,000	$ 17,051,000	$ 36,367,000	$ 52,768,000