Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Commissions	$ 355,282	$ 332,307	$ 266,221
Information services	25,807	23,269	22,585
Post-trade services	11,090	10,812	11,648
Investment income	3,619	2,137	905
Other	1,673	1,394	1,739
Total revenues	397,471	369,919	303,098
Expenses
Employee compensation and benefits	102,751	96,785	83,856
Depreciation and amortization	19,274	17,838	18,542
Technology and communications	20,048	17,275	15,916
Professional and consulting fees	19,367	17,175	13,043
Occupancy	6,125	4,681	4,685
Marketing and advertising	9,762	8,934	6,148
Clearing costs	5,797	6,060	3,313
General and administrative	12,579	9,569	9,695
Total expenses	195,703	178,317	155,198
Income before income taxes	201,768	191,602	147,900
Provision for income taxes	53,679	65,430	51,863
Net income	$ 148,089	$ 126,172	$ 96,037
Net income per common share
Basic	$ 4.02	$ 3.42	$ 2.62
Diluted	3.89	3.34	2.55
Cash dividends declared per common share	$ 1.32	$ 1.04	$ 0.80
Weighted average shares outstanding
Basic	36,864	36,844	36,690
Diluted	38,038	37,738	37,637