Revenue Recognition (Schedule of Major Revenue Categories) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Trading Execution and Clearing Services
Commissions and fees	$ 1,864,000	$ 2,674,000
Principal transactions	1,610,000	2,941,000
Advisory fees and additional income	183,000	27,000
Margin interest, marketing and distribution fees
Margin interest	2,066,000	1,635,000
12b1 fees	706,000	900,000
Total Margin interest, marketing and distribution fees	2,772,000	2,535,000
Total revenue	$ 6,429,000	$ 8,177,000