Revenue Recognition (Schedule of Major Revenue Categories) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Trading Execution and Clearing Services
Commissions and fees	$ 1,925,000	$ 2,347,000	$ 6,030,000	$ 7,380,000
Principal transactions	2,041,000	2,634,000	5,479,000	7,838,000
Advisory fees and additional income	234,000	172,000	626,000	378,000
Margin interest, marketing and distribution fees
Margin interest	2,151,000	1,943,000	6,254,000	5,454,000
12b1 fees	793,000	788,000	2,245,000	2,499,000
Total Margin interest, marketing and distribution fees	2,944,000	2,731,000	8,499,000	7,953,000
Total Revenue	$ 7,144,000	$ 7,884,000	$ 20,634,000	$ 23,549,000