Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues
Revenues	$ 162,093	$ 164,006	$ 533,891	$ 517,779
Expenses
Employee compensation and benefits	40,878	37,583	129,698	120,413
Depreciation and amortization	13,964	9,032	38,840	25,404
Technology and communications	10,665	8,417	31,245	25,170
Professional and consulting fees	10,847	8,269	31,191	22,009
Occupancy	3,265	3,445	9,882	10,205
Marketing and advertising	1,821	1,148	6,153	5,633
Clearing costs	3,269	4,838	12,335	16,061
General and administrative	3,381	3,467	9,893	9,853
Total expenses	88,090	76,199	269,237	234,748
Operating income	74,003	87,807	264,654	283,031
Other income (expense)
Investment income	108	344	322	2,327
Interest expense	(314)	(1,046)	(676)	(1,046)
Other, net	697	860	(1,952)	(242)
Total other income (expense)	491	158	(2,306)	1,039
Income before income taxes	74,494	87,965	262,348	284,070
Provision for income taxes	16,536	20,189	56,645	57,624
Net income	$ 57,958	$ 67,776	$ 205,703	$ 226,446
Net income per common share
Basic	$ 1.54	$ 1.81	$ 5.49	$ 6.06
Diluted	1.52	1.78	5.40	5.94
Cash dividends declared per common share	$ 0.66	$ 0.60	$ 1.98	$ 1.80
Weighted average shares outstanding
Basic	37,529	37,386	37,502	37,343
Diluted	38,084	38,160	38,114	38,129
Commissions [Member]
Revenues
Revenues	$ 142,826	$ 150,586	$ 475,095	$ 478,632
Information Services [Member]
Revenues
Revenues	9,608	8,501	28,614	25,570
Post-trade Services [Member]
Revenues
Revenues	9,444	4,689	29,553	12,896
Other [Member]
Revenues
Revenues	$ 215	$ 230	$ 629	$ 681