CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net income (loss) attributable to non-controlling interests	$ 30,272,000	$ 32,110,000	$ 158,964,000
Adjustments to reconcile net income to net cash provided by (used in) operating activities
Depreciation and amortization of furniture, equipment and leasehold improvements	9,924,000	7,605,000	7,994,000
Deferred income taxes	6,457,000	(14,616,000)	(792,000)
Amortization of notes receivable	15,966,000	13,741,000	13,427,000
Amortization of debt issuance costs	219,000	248,000	250,000
Write-off of debt issuance costs	5,000	61,000	0
Provision for (reversal of) credit losses	(5,000)	(2,955,000)	2,896,000
Share-based compensation	16,940,000	15,914,000	31,138,000
Amortization of right-of-use lease assets	27,281,000	26,804,000	26,125,000
Gain on repurchase of senior secured notes	(51,000)	(235,000)	0
Decrease (increase) in operating assets:
Deposits with clearing organizations	(1,015,000)	(10,723,000)	16,375,000
Receivable from brokers, dealers and clearing organizations	(78,619,000)	(36,175,000)	33,592,000
Receivable from customers	142,877,000	21,641,000	(113,511,000)
Income tax receivable	(7,199,000)	0	0
Securities purchased under agreements to resell	(5,842,000)	935,000	(935,000)
Securities owned	(296,718,000)	135,910,000	(23,987,000)
Notes receivable	(21,111,000)	(17,253,000)	(21,249,000)
Other assets	(11,246,000)	16,412,000	65,814,000
Increase (decrease) in operating liabilities:
Drafts payable	9,002,000	0	0
Payable to brokers, dealers and clearing organizations	(188,116,000)	127,949,000	162,146,000
Payable to customers	(87,188,000)	(483,000)	(45,849,000)
Securities sold under agreements to repurchase	479,373,000	(116,313,000)	(65,116,000)
Securities sold but not yet purchased	(21,092,000)	(19,190,000)	(54,213,000)
Accrued compensation	13,227,000	(107,350,000)	23,238,000
Income tax payable	(4,130,000)	(9,406,000)	3,810,000
Accounts payable and other liabilities	(48,021,000)	(139,000)	7,669,000
Cash provided by/(used in) operating activities	(18,810,000)	64,492,000	227,786,000
Cash flows from investing activities
Purchase of furniture, equipment and leasehold improvements	(17,056,000)	(16,311,000)	(8,268,000)
Acquisition of BondWave LLC, net of cash consideration	(2,929,000)	0	0
Proceeds from the settlement of Company-owned life insurance	4,424,000	2,174,000	2,001,000
Cash used in investing activities	(15,561,000)	(14,137,000)	(6,267,000)
Cash flows from financing activities
Cash dividends paid on Class A non-voting and Class B voting common stock	(6,452,000)	(7,044,000)	(19,444,000)
Issuance of Class A non-voting common stock	75,000	127,000	58,000
Repurchase of Class A non-voting common stock for cancellation	(35,124,000)	(60,636,000)	(7,737,000)
Payments for employee taxes withheld related to vested share-based awards	(5,907,000)	(2,283,000)	(4,967,000)
Payment of Company sponsored Initial Public Offering costs	0	0	(454,000)
Contributions from non-controlling interests	0	0	3,147,000
Proceeds from Company sponsored Initial Public Offering	0	0	126,500,000
Distribution to non-controlling interests	(198,000)	(90,000)	0
Redemption on redeemable non-controlling interests	(26,155,000)	(103,536,000)	0
Repurchase of senior secured notes	(1,000,000)	(10,950,000)	0
Debt issuance costs	0	0	(22,000)
Decrease in bank call loans, net	0	(69,500,000)	(12,500,000)
Cash provided by/(used in) financing activities	(74,761,000)	(253,912,000)	84,581,000
Net increase/(decrease) in cash and cash equivalents and restricted cash	(109,132,000)	(203,557,000)	306,100,000
Cash and cash equivalents and restricted cash, beginning of year	137,967,000	341,524,000	35,424,000
Cash and cash equivalents and restricted cash, end of year	28,835,000	137,967,000	341,524,000
Reconciliation of cash and cash equivalents and restricted cash within the consolidated balance sheet:
Cash and cash equivalents	28,835,000	112,433,000	213,759,000
Restricted cash	0	25,534,000	127,765,000
Total cash and cash equivalents and restricted cash	28,835,000	137,967,000	341,524,000
Schedule of non-cash financing activities
Employee share plan issuance	9,376,000	4,288,000	7,361,000
Fair value of non-cash assets acquired	6,658,000	0	0
Fair value of liabilities assumed in acquisition	1,544,000	0	0
Contingent consideration for BondWave LLC	(1,395,000)	0	0
Supplemental disclosure of cash flow information
Cash paid during the year for interest	68,399,000	22,810,000	10,089,000
Cash paid during the year for income taxes, net	$ 20,576,000	$ 37,512,000	$ 62,378,000