Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues
Revenues	$ 752,547	$ 718,300	$ 698,951
Expenses
Employee compensation and benefits	206,926	182,104	170,916
Depreciation and amortization	70,557	61,446	53,447
Technology and communications	62,801	52,964	42,474
Professional and consulting fees	31,935	33,949	41,925
Occupancy	14,216	14,121	13,320
Marketing and advertising	11,049	9,977	9,059
Clearing costs	17,002	17,663	16,074
General and administrative	23,042	19,200	14,501
Total expenses	437,528	391,424	361,716
Operating income	315,019	326,876	337,235
Other income (expense)
Interest income	22,425	5,040	401
Interest expense	(1,983)	(700)	(842)
Equity in earnings of unconsolidated affiliate	735	1,126	0
Other, net	(3,496)	5,946	(2,871)
Total other income (expense)	17,681	11,412	(3,312)
Income before income taxes	332,700	338,288	333,923
Provision for income taxes	74,645	88,064	76,035
Net income	$ 258,055	$ 250,224	$ 257,888
Net income per common share
Basic	$ 6.87	$ 6.68	$ 6.88
Diluted	6.85	6.65	6.77
Cash dividends declared per common share	$ 2.88	$ 2.8	$ 2.64
Weighted average shares outstanding
Basic	37,546	37,468	37,508
Diluted	37,654	37,643	38,097
Commissions [Member]
Revenues
Revenues	$ 662,964	$ 641,183	$ 621,008
Information Services [Member]
Revenues
Revenues	46,383	39,314	38,175
Post-trade Services [Member]
Revenues
Revenues	40,178	36,877	38,922
Technology Services [Member]
Revenues
Revenues	$ 3,022	$ 926	$ 846