Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Revenues	$ 164,006	$ 131,597	$ 517,779	$ 381,578
Expenses
Employee compensation and benefits	37,583	32,681	120,413	97,962
Depreciation and amortization	9,032	6,700	25,404	19,127
Technology and communications	8,417	7,381	25,170	19,637
Professional and consulting fees	8,269	7,018	22,009	19,145
Occupancy	3,445	2,802	10,205	8,549
Marketing and advertising	1,148	2,506	5,633	8,472
Clearing costs	4,838	2,782	16,061	7,969
General and administrative	3,467	3,762	9,853	10,686
Total expenses	76,199	65,632	234,748	191,547
Operating income	87,807	65,965	283,031	190,031
Other income (expense)
Investment income	344	2,211	2,327	6,296
Interest expense	(1,046)		(1,046)
Other, net	860	(838)	(242)	(860)
Total other income (expense)	158	1,373	1,039	5,436
Income before income taxes	87,965	67,338	284,070	195,467
Provision for income taxes	20,189	13,336	57,624	40,838
Net income	$ 67,776	$ 54,002	$ 226,446	$ 154,629
Net income per common share
Basic	$ 1.81	$ 1.46	$ 6.06	$ 4.17
Diluted	1.78	1.42	5.94	4.08
Cash dividends declared per common share	$ 0.60	$ 0.51	$ 1.80	$ 1.53
Weighted average shares outstanding
Basic	37,386	37,066	37,343	37,053
Diluted	38,160	37,995	38,129	37,913
Commissions [Member]
Revenues
Revenues	$ 150,586	$ 119,869	$ 478,632	$ 346,753
Information Services [Member]
Revenues
Revenues	8,501	7,693	25,570	22,215
Post-trade Services [Member]
Revenues
Revenues	4,689	3,784	12,896	11,840
Other [Member]
Revenues
Revenues	$ 230	$ 251	$ 681	$ 770