Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues
Revenues	$ 184,795	$ 125,490	$ 353,773	$ 249,981
Expenses
Employee compensation and benefits	41,636	32,623	82,830	65,281
Depreciation and amortization	8,305	6,345	16,372	12,427
Technology and communications	8,592	6,474	16,753	12,256
Professional and consulting fees	8,065	6,296	13,740	12,127
Occupancy	3,286	2,798	6,760	5,747
Marketing and advertising	1,810	3,667	4,485	5,966
Clearing costs	5,713	2,610	11,223	5,187
General and administrative	3,253	3,800	6,386	6,924
Total expenses	80,660	64,613	158,549	125,915
Operating income	104,135	60,877	195,224	124,066
Other income (expense)
Investment income	714	2,096	1,983	4,085
Other, net	(446)	(64)	(1,102)	(22)
Total other income	268	2,032	881	4,063
Income before income taxes	104,403	62,909	196,105	128,129
Provision for income taxes	20,549	14,804	37,435	27,502
Net income	$ 83,854	$ 48,105	$ 158,670	$ 100,627
Net income per common share
Basic	$ 2.25	$ 1.30	$ 4.25	$ 2.72
Diluted	2.20	1.27	4.16	2.66
Cash dividends declared per common share	$ 0.60	$ 0.51	$ 1.20	$ 1.02
Weighted average shares outstanding
Basic	37,340	37,049	37,322	37,046
Diluted	38,153	37,910	38,115	37,871
Commissions [Member]
Revenues
Revenues	$ 172,092	$ 114,124	$ 328,046	$ 226,884
Information Services [Member]
Revenues
Revenues	8,427	7,156	17,069	14,522
Post-trade Services [Member]
Revenues
Revenues	4,054	3,956	8,207	8,056
Other [Member]
Revenues
Revenues	$ 222	$ 254	$ 451	$ 519