Revenue Recognition (Schedule of Major Revenue Categories) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Trading Execution and Clearing Services
Commissions and fees	$ 2,303,000	$ 2,376,000	$ 4,105,000	$ 5,033,000
Principal transactions	1,766,000	2,263,000	3,438,000	5,204,000
Advisory fees and additional income	209,000	162,000	392,000	206,000
Margin interest, marketing and distribution fees
Margin interest	2,037,000	1,876,000	4,103,000	3,511,000
12b1 fees	746,000	811,000	1,452,000	1,711,000
Total Margin interest, marketing and distribution fees	2,783,000	2,687,000	5,555,000	5,222,000
Total Revenue	$ 7,061,000	$ 7,488,000	$ 13,490,000	$ 15,665,000