CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
REVENUES
Commissions and fees	$ 572,932		$ 472,068		$ 1,190,395	$ 972,406
Investment income	1,525		731		2,606	1,332
Other income, net	762		388		1,498	910
Total revenues	575,219		473,187		1,194,499	974,648
EXPENSES
Employee compensation and benefits	309,610		251,958		642,447	522,857
Other operating expenses	98,050		83,694		186,833	160,007
(Gain)/loss on disposal	(1,016)		(230)		(511)	(2,650)
Amortization	25,954		20,785		52,146	41,324
Depreciation	5,666		5,599		11,701	11,151
Interest	16,293		10,052		31,491	19,723
Change in estimated acquisition earn-out payables	(2,860)		419		(1,650)	2,885
Total expenses	451,697		372,277		922,457	755,297
Income before income taxes	123,522		100,910		272,042	219,351
Income taxes	30,929		26,988		65,553	54,601
Net income	$ 92,593	$ 113,896	$ 73,922	$ 90,828	$ 206,489	$ 164,750
Net income per share:
Basic (in dollars per share)	$ 0.33		$ 0.27		$ 0.73	$ 0.60
Diluted (in dollars per share)	0.33		0.26		0.73	0.58
Dividends declared per share (in dollars per share)	$ 0.080		$ 0.075		$ 0.160	$ 0.150