Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues
Revenues	$ 176,334	$ 184,795	$ 371,798	$ 353,773
Expenses
Employee compensation and benefits	40,732	41,636	88,820	82,830
Depreciation and amortization	13,097	8,305	24,876	16,372
Technology and communications	10,544	8,592	20,580	16,753
Professional and consulting fees	10,704	8,065	20,344	13,740
Occupancy	3,300	3,286	6,617	6,760
Marketing and advertising	3,128	1,810	4,332	4,485
Clearing costs	4,372	5,713	9,066	11,223
General and administrative	3,280	3,253	6,512	6,386
Total expenses	89,157	80,660	181,147	158,549
Operating income	87,177	104,135	190,651	195,224
Other income (expense)
Investment income	107	714	214	1,983
Interest expense	(171)		(362)
Other, net	(1,060)	(446)	(2,649)	(1,102)
Total other income (expense)	(1,124)	268	(2,797)	881
Income before income taxes	86,053	104,403	187,854	196,105
Provision for income taxes	18,765	20,549	40,109	37,435
Net income	$ 67,288	$ 83,854	$ 147,745	$ 158,670
Net income per common share
Basic	$ 1.79	$ 2.25	$ 3.94	$ 4.25
Diluted	1.77	2.20	3.87	4.16
Cash dividends declared per common share	$ 0.66	$ 0.60	$ 1.32	$ 1.20
Weighted average shares outstanding
Basic	37,508	37,340	37,489	37,322
Diluted	38,104	38,153	38,129	38,115
Commissions [Member]
Revenues
Revenues	$ 156,431	$ 172,092	$ 332,269	$ 328,046
Information Services [Member]
Revenues
Revenues	9,844	8,427	19,006	17,069
Post-trade Services [Member]
Revenues
Revenues	9,848	4,054	20,109	8,207
Other [Member]
Revenues
Revenues	$ 211	$ 222	$ 414	$ 451