Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Revenues	$ 698,951	$ 689,125	$ 511,352
Expenses
Employee compensation and benefits	170,916	156,885	131,079
Depreciation and amortization	53,447	35,996	26,857
Technology and communications	42,474	34,092	26,792
Professional and consulting fees	41,925	32,304	25,534
Occupancy	13,320	13,425	11,639
Marketing and advertising	9,059	7,940	11,559
Clearing costs	16,074	21,058	11,314
General and administrative	14,501	12,697	15,696
Total expenses	361,716	314,397	260,470
Operating income (loss)	337,235	374,728	250,882
Other income (expense)
Investment income	401	2,446	8,063
Interest expense	(842)	(1,142)
Other, net	(2,871)	(1,673)	(1,521)
Total other income (expense)	(3,312)	(369)	6,542
Income before income taxes	333,923	374,359	257,424
Provision for income taxes	76,035	74,982	52,522
Net income	$ 257,888	$ 299,377	$ 204,902
Net income per common share
Basic	$ 6.88	$ 8.01	$ 5.53
Diluted	6.77	7.85	5.40
Cash dividends declared per common share	$ 2.64	$ 2.40	$ 2.04
Weighted average shares outstanding
Basic	37,508	37,359	37,083
Diluted	38,097	38,144	37,956
Commissions [Member]
Revenues
Revenues	$ 621,008	$ 634,445	$ 463,856
Information Services [Member]
Revenues
Revenues	38,175	34,341	30,730
Post-trade Services [Member]
Revenues
Revenues	38,922	19,460	15,763
Other [Member]
Revenues
Revenues	$ 846	$ 879	$ 1,003