Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Statement of Cash Flows [Abstract]
Net Income (Loss) Attributable to Parent	$ 41,106,000	$ 27,518,000
Non-cash items included in net income:
Depreciation and amortization of furniture, equipment and leasehold improvements	6,169,000	5,575,000
Deferred income taxes	7,254,000	422,000
Amortization of notes receivable	8,736,000	9,679,000
Amortization of debt issuance costs	149,000	187,000
Write-off of debt issuance costs	341,000	184,000
Provision for credit losses	33,000	55,000
Share-based compensation	4,877,000	11,858,000
Amortization of right-of-use lease assets	18,747,000	19,141,000
Gain on repurchase of senior secured notes	(86,000)	0
Decrease (increase) in operating assets:
Deposits with clearing organizations	28,787,000	6,052,000
Receivable from brokers, dealers and clearing organizations	(43,963,000)	8,759,000
Receivable from customers	(298,134,000)	(34,205,000)
Income tax receivable	2,178,000	(1,319,000)
Securities purchased under agreements to resell	0	290,000
Securities owned	153,039,000	184,390,000
Notes receivable	(9,789,000)	(9,541,000)
Other assets	17,449,000	(11,980,000)
Increase (decrease) in operating liabilities:
Drafts payable	18,251,000	1,446,000
Payable to brokers, dealers and clearing organizations	(154,026,000)	75,388,000
Payable to customers	46,011,000	(23,560,000)
Securities sold under agreements to repurchase	(34,438,000)	(230,498,000)
Securities sold but not yet purchased	121,878,000	36,434,000
Accrued compensation	(4,856,000)	(23,273,000)
Accounts payable and other liabilities	(20,522,000)	(18,001,000)
Cash (used in)/provided by operating activities	(148,383,000)	22,897,000
Cash flows from investing activities
Purchase of furniture, equipment and leasehold improvements	(3,708,000)	(8,672,000)
Proceeds from Insurance Settlement, Investing Activities	0	1,720,000
Cash used in investing activities	(3,708,000)	(6,952,000)
Cash flows from financing activities
Cash dividends paid on Class A non-voting and Class B voting common stock	(4,597,000)	(4,408,000)
Proceeds from Issuance or Sale of Equity	34,000	83,000
Repurchase of Class A non-voting common stock for cancellation	(14,228,000)	(8,400,000)
Payments for employee taxes withheld related to vested share-based awards	(5,771,000)	(1,014,000)
Proceeds from Issuance of Secured Debt	125,000,000	0
Repayments of Secured Debt	148,574,000	50,000,000
Repurchase of Secured Debt	1,426,000	0
Payments of Debt Issuance Costs	210,000	0
Payment for Debt Extinguishment or Debt Prepayment Cost	2,507,000	1,688,000
Increase in bank call loans, net	156,900,000	(15,000,000)
Cash provided by/(used in) financing activities	104,621,000	(80,427,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(47,470,000)	(64,482,000)
Cash and cash equivalents, beginning of period	79,550,000	90,675,000
Cash and cash equivalents, end of period	32,080,000	26,193,000
Schedule of non-cash financing activities
Employee share plan issuance	11,940,000	1,484,000
Supplemental disclosure of cash flow information
Interest Paid, Excluding Capitalized Interest, Operating Activities	17,929,000	37,710,000
Cash paid during the period for income taxes, net	$ 5,918,000	$ 13,506,000