Acquisitions (Schedule of Assets Acquired and Liabilities Assumed) (Details) - StockCross [Member]	Dec. 31, 2019 USD ($)
Assets acquired
Cash and cash equivalents	$ 1,588,000
Cash and securities segregated for regulatory purposes	224,814,000
Receivables from customers	86,331,000
Receivables from broker-dealers and clearing organizations	3,105,000
Other receivables	627,000
Prepaid expenses and other assets	346,000
Securities borrowed	193,529,000
Securities owned, at fair value	3,018,000
Furniture, equipment and leasehold improvements, net	19,000
Lease right-of-use assets	1,141,000
Deferred tax assets	407,000
Total Assets acquired	514,925,000
Liabilities assumed
Payables to customers	308,091,000
Payables to non-customers	9,151,000
Drafts payable	2,834,000
Payables to broker-dealers and clearing organizations	1,406,000
Accounts payable and accrued liabilities	963,000
Securities loaned	170,443,000
Securities sold, not yet purchased, at fair value	28,000
Notes payable - related party	5,000,000
Lease liabilities	1,295,000
Total Liabilities assumed	499,211,000
Net Assets acquired	$ 15,714,000