CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
REVENUES
Commissions and fees	$ 1,857,270	$ 1,762,787	$ 1,656,951
Investment income	1,626	1,456	1,004
Other income, net	22,451	2,386	2,554
Total revenues	1,881,347	1,766,629	1,660,509
EXPENSES
Employee compensation and benefits	994,652	925,217	856,952
Non-cash stock-based compensation	30,631	16,052	15,513
Other operating expenses	283,470	262,872	251,055
(Gain)/loss on disposal	(2,157)	(1,291)	(619)
Amortization	85,446	86,663	87,421
Depreciation	22,698	21,003	20,890
Interest	38,316	39,481	39,248
Change in estimated acquisition earn-out payables	9,200	9,185	3,003
Total expenses	1,431,625	1,343,130	1,257,950
Income before income taxes	449,722	423,499	402,559
Income taxes	50,092	166,008	159,241
Net income	$ 399,630	$ 257,491	$ 243,318
Net income per share:
Basic (in dollars per share)	$ 2.86	$ 1.84	$ 1.72
Diluted (in dollars per share)	2.81	1.82	1.70
Dividends declared per share (in dollars per share)	$ 0.56	$ 0.50	$ 0.45