Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues
Revenues	$ 195,464	$ 168,978
Expenses
Employee compensation and benefits	48,088	41,194
Depreciation and amortization	11,779	8,067
Technology and communications	10,036	8,161
Professional and consulting fees	9,640	5,675
Occupancy	3,317	3,474
Marketing and advertising	1,204	2,675
Clearing costs	4,694	5,510
General and administrative	3,232	3,133
Total expenses	91,990	77,889
Operating income	103,474	91,089
Other income (expense)
Investment income	107	1,269
Interest expense	(191)
Other, net	(1,589)	(656)
Total other income (expense)	(1,673)	613
Income before income taxes	101,801	91,702
Provision for income taxes	21,344	16,886
Net income	$ 80,457	$ 74,816
Net income per common share
Basic	$ 2.15	$ 2.01
Diluted	2.11	1.96
Cash dividends declared per common share	$ 0.66	$ 0.60
Weighted average shares outstanding
Basic	37,470	37,303
Diluted	38,155	38,075
Commissions [Member]
Revenues
Revenues	$ 175,838	$ 155,954
Information Services [Member]
Revenues
Revenues	9,162	8,642
Post-trade Services [Member]
Revenues
Revenues	10,261	4,153
Other [Member]
Revenues
Revenues	$ 203	$ 229