Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Revenues	$ 106,964	$ 96,314	$ 221,678	$ 199,278
Expenses
Employee compensation and benefits	26,199	25,319	55,033	52,603
Depreciation and amortization	5,790	4,790	11,059	9,483
Technology and communications	5,793	4,822	11,572	9,407
Professional and consulting fees	5,426	4,086	10,483	8,365
Occupancy	3,467	1,422	6,804	2,826
Marketing and advertising	3,535	2,782	5,600	4,668
Clearing costs	2,012	1,517	3,737	2,844
General and administrative	2,708	2,591	5,183	4,939
Total expenses	54,930	47,329	109,471	95,135
Operating income	52,034	48,985	112,207	104,143
Other income (expense)
Investment income	1,383	840	2,551	1,587
Other, net	(207)	(252)	(535)	(550)
Total other income	1,176	588	2,016	1,037
Income before income taxes	53,210	49,573	114,223	105,180
Provision for income taxes	12,723	11,550	25,796	24,694
Net income	$ 40,487	$ 38,023	$ 88,427	$ 80,486
Net income per common share
Basic	$ 1.10	$ 1.03	$ 2.39	$ 2.18
Diluted	1.07	1.00	2.33	2.11
Cash dividends declared per common share	$ 0.42	$ 0.33	$ 0.84	$ 0.66
Weighted average shares outstanding
Basic	36,950	36,853	36,952	36,852
Diluted	37,862	38,077	37,874	38,095
Commissions [Member]
Revenues
Revenues	$ 96,113	$ 87,015	$ 198,885	$ 181,037
Information Services [Member]
Revenues
Revenues	6,930	6,497	13,996	12,682
Post-trade Services [Member]
Revenues
Revenues	3,620	2,489	8,196	4,945
Other [Member]
Revenues
Revenues	$ 301	$ 313	$ 601	$ 614