Revenue Recognition (Schedule of Major Revenue Categories) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Trading Execution and Clearing Services
Commissions and fees	$ 1,853,000	$ 4,325,000	$ 4,193,000	$ 11,333,000
Principal transactions and proprietary trading	1,081,000	4,107,000	814,000	8,355,000
Market making	535,000	1,758,000	1,299,000	3,372,000
Stock borrow / stock loan	4,148,000	2,240,000	7,726,000	4,087,000
Advisory fees	476,000	403,000	983,000	759,000
Total Trading Execution and Clearing Services	8,093,000	12,833,000	15,015,000	27,906,000
Other Income
Interest	572,000	1,163,000	807,000	2,317,000
Margin interest	2,201,000	2,296,000	4,168,000	4,448,000
12b-1 fees	378,000	164,000	538,000	317,000
Total Interest, marketing and distribution fees	3,151,000	3,623,000	5,513,000	7,082,000
Other income	479,000	337,000	1,503,000	729,000
Total Revenue	$ 11,723,000	$ 16,793,000	$ 22,031,000	$ 35,717,000