Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues
Revenues	$ 125,490	$ 106,964	$ 249,981	$ 221,678
Expenses
Employee compensation and benefits	32,623	26,199	65,281	55,033
Depreciation and amortization	6,345	5,790	12,427	11,059
Technology and communications	6,474	5,793	12,256	11,572
Professional and consulting fees	6,296	5,426	12,127	10,483
Occupancy	2,798	3,467	5,747	6,804
Marketing and advertising	3,667	3,535	5,966	5,600
Clearing costs	2,610	2,012	5,187	3,737
General and administrative	3,800	2,708	6,924	5,183
Total expenses	64,613	54,930	125,915	109,471
Operating income	60,877	52,034	124,066	112,207
Other income (expense)
Investment income	2,096	1,383	4,085	2,551
Other, net	(64)	(207)	(22)	(535)
Total other income	2,032	1,176	4,063	2,016
Income before income taxes	62,909	53,210	128,129	114,223
Provision for income taxes	14,804	12,723	27,502	25,796
Net income	$ 48,105	$ 40,487	$ 100,627	$ 88,427
Net income per common share
Basic	$ 1.30	$ 1.10	$ 2.72	$ 2.39
Diluted	1.27	1.07	2.66	2.33
Cash dividends declared per common share	$ 0.51	$ 0.42	$ 1.02	$ 0.84
Weighted average shares outstanding
Basic	37,049	36,950	37,046	36,952
Diluted	37,910	37,862	37,871	37,874
Commissions [Member]
Revenues
Revenues	$ 114,124	$ 96,113	$ 226,884	$ 198,885
Information Services [Member]
Revenues
Revenues	7,156	6,930	14,522	13,996
Post-trade Services [Member]
Revenues
Revenues	3,956	3,620	8,056	8,196
Other [Member]
Revenues
Revenues	$ 254	$ 301	$ 519	$ 601