Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Statement of Cash Flows [Abstract]
Net Income (Loss) Attributable to Parent	$ 25,467,000	$ 23,569,000
Non-cash items included in net income:
Depreciation and amortization of furniture, equipment and leasehold improvements	4,120,000	3,602,000
Deferred income taxes	4,853,000	1,081,000
Amortization of notes receivable	5,797,000	6,469,000
Amortization of debt issuance costs	97,000	129,000
Write-off of debt issuance costs	4,000	0
Provision for credit losses	(42,000)	34,000
Share-based compensation	2,395,000	6,384,000
Amortization of right-of-use lease assets	12,411,000	12,892,000
Gain on repurchase of senior secured notes	(86,000)	0
Decrease (increase) in operating assets:
Deposits with clearing organizations	42,121,000	(2,187,000)
Receivable from brokers, dealers and clearing organizations	(152,654,000)	(1,438,000)
Receivable from customers	(63,164,000)	(86,838,000)
Income tax receivable	3,381,000	1,014,000
Securities purchased under agreements to resell	0	251,000
Securities owned	297,690,000	(157,786,000)
Notes receivable	(6,241,000)	(5,824,000)
Other assets	28,524,000	(19,359,000)
Increase (decrease) in operating liabilities:
Drafts payable	37,374,000	1,108,000
Payable to brokers, dealers and clearing organizations	(304,864,000)	129,512,000
Payable to customers	82,179,000	(10,862,000)
Income taxes payable	0	849,000
Securities sold under agreements to repurchase	(133,110,000)	37,619,000
Securities sold but not yet purchased	256,018,000	70,533,000
Accrued compensation	(58,946,000)	(38,827,000)
Accounts payable and other liabilities	(14,995,000)	(14,290,000)
Cash used in operating activities	(15,913,000)	(37,991,000)
Cash flows from investing activities
Purchase of furniture, equipment and leasehold improvements	(3,161,000)	(6,941,000)
Proceeds from Insurance Settlement, Investing Activities	0	695,000
Cash used in investing activities	(3,161,000)	(6,246,000)
Cash flows from financing activities
Cash dividends paid on Class A non-voting and Class B voting common stock	(3,089,000)	(2,865,000)
Repurchase of Class A non-voting common stock for cancellation	(12,266,000)	(6,352,000)
Payments for employee taxes withheld related to vested share-based awards	(5,458,000)	(1,014,000)
Repurchase of Secured Debt	1,426,000	0
Increase in bank call loans, net	13,000,000	35,100,000
Cash used in (provided by) financing activities	(9,239,000)	24,869,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(28,313,000)	(19,368,000)
Cash and cash equivalents, beginning of period	79,550,000	90,675,000
Cash and cash equivalents, end of period	51,237,000	71,307,000
Schedule of non-cash financing activities
Employee share plan issuance	10,582,000	1,706,000
Supplemental disclosure of cash flow information
Interest Paid, Excluding Capitalized Interest, Operating Activities	14,727,000	25,830,000
Cash paid during the period for income taxes, net	$ 1,049,000	$ 7,326,000