4. Revenue Recognition (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Total revenue from Principal transactions	$ 2,263,000	$ 98,000	$ 5,204,000	$ 206,000
Total revenue from Commissions and fees	2,512,000	1,037,000	5,186,000	2,219,000
Total revenue from Margin interest, marketing and distribution fees	2,687,000	1,545,000	5,222,000	2,626,000
Interest and dividends - non StockCross	24,000	3,000	35,000	5,000
Advisory fees - non StockCross	2,000	6,000	18,000	12,000
Total Revenue	7,488,000	2,689,000	15,665,000	5,068,000
Principal transactions | non StockCross
Total revenue from Principal transactions	505,000	98,000	1,077,000	206,000
Principal transactions | Assets acquired from StockCross
Total revenue from Principal transactions	1,758,000	0	4,127,000	0
Commissions and fees | non StockCross
Total revenue from Commissions and fees	2,162,000	1,037,000	4,117,000	2,219,000
Commissions and fees | Assets acquired from StockCross
Total revenue from Commissions and fees	350,000	0	1,069,000	0
Margin interest, marketing and distribution fees | non StockCross
Total revenue from Margin interest, marketing and distribution fees	2,312,000	1,545,000	4,640,000	2,626,000
Margin interest, marketing and distribution fees | Assets acquired from StockCross
Total revenue from Margin interest, marketing and distribution fees	$ 375,000	$ 0	$ 582,000	$ 0