Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Commissions	$ 266,221	$ 221,138	$ 203,652
Information and post-trade services	30,660	31,510	25,377
Technology products and services	3,573	6,874	6,331
Investment income	905	543	420
Other	1,739	2,709	2,953
Total revenues	303,098	262,774	238,733
Expenses
Employee compensation and benefits	83,856	74,995	64,406
Depreciation and amortization	18,542	17,379	14,123
Technology and communications	15,916	17,685	16,037
Professional and consulting fees	13,043	14,375	18,220
Occupancy	4,685	4,381	5,173
Marketing and advertising	6,148	5,769	4,632
General and administrative	13,008	9,654	8,862
Total expenses	155,198	144,238	131,453
Income before income taxes from continuing operations	147,900	118,536	107,280
Provision for income taxes	51,863	43,730	38,717
Net income from continuing operations	96,037	74,806	68,563
Loss from discontinued operations, net of income taxes			(189)
Gain on the sale of discontinued operations, net of tax benefit			7,642
Net income	$ 96,037	$ 74,806	$ 76,016
Basic earnings per common share
Income from continuing operations	$ 2.62	$ 2.03	$ 1.86
Income from discontinued operations			0.20
Net income per common share	2.62	2.03	2.06
Diluted earnings per common share
Income from continuing operations	2.55	1.97	1.81
Income from discontinued operations			0.20
Net income per common share	2.55	1.97	2.01
Cash dividends declared per common share	$ 0.80	$ 0.64	$ 0.52
Weighted average shares outstanding
Basic	36,690	36,930	36,886
Diluted	37,637	37,889	37,888