Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Commissions	$ 332,307	$ 266,221	$ 221,138
Information and post-trade services	31,225	30,660	31,510
Investment income	2,137	905	543
Other	4,250	5,312	9,583
Total revenues	369,919	303,098	262,774
Expenses
Employee compensation and benefits	96,785	83,856	74,995
Depreciation and amortization	17,838	18,542	17,379
Technology and communications	17,275	15,916	17,685
Professional and consulting fees	17,175	13,043	14,375
Occupancy	4,681	4,685	4,381
Marketing and advertising	8,934	6,148	5,769
General and administrative	15,629	13,008	9,654
Total expenses	178,317	155,198	144,238
Income before income taxes	191,602	147,900	118,536
Provision for income taxes	65,430	51,863	43,730
Net income	$ 126,172	$ 96,037	$ 74,806
Net income per common share
Basic	$ 3.42	$ 2.62	$ 2.03
Diluted	3.34	2.55	1.97
Cash dividends declared per common share	$ 1.04	$ 0.80	$ 0.64
Weighted average shares outstanding
Basic	36,844	36,690	36,930
Diluted	37,738	37,637	37,889