STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenue
Management fee revenue, net	$ 1,662,625	$ 1,567,431	$ 1,475,511
Service agreement revenue	29,149	29,200	29,997
Total operating revenue	1,691,774	1,596,631	1,505,508
Operating expenses
Commissions	947,481	893,800	847,880
Salaries and employee benefits	240,181	213,356	226,713
All other operating expenses	215,740	197,111	198,374
Total operating expenses	1,403,402	1,304,267	1,272,967
Operating income	288,372	292,364	232,541
Investment income
Net investment income	24,608	20,547	17,791
Net realized investment gains	1,334	672	492
Net impairment losses recognized in earnings	(182)	(416)	(1,558)
Equity in earnings of limited partnerships	2,801	7,025	16,983
Total investment income	28,561	27,828	33,708
Interest expense, net	1,238	101
Income before income taxes	315,695	320,091	266,249
Income tax expense	118,696	109,725	91,571
Net income	$ 196,999	$ 210,366	$ 174,678
Class A
Net income per share
Common stock - basic (in dollars per share)	$ 4.23	$ 4.52	$ 3.75
Common stock - diluted (in dollars per share)	$ 3.76	$ 4.01	$ 3.33
Weighted average shares outstanding – Basic
Common stock - basic (in shares)	46,186,831	46,188,952	46,186,671
Weighted average shares outstanding – Diluted
Common stock - diluted (in shares)	52,337,463	52,435,303	52,498,811
Class B
Net income per share
Common stock - basic (in dollars per share)	$ 635	$ 678	$ 563
Common stock - diluted (in dollars per share)	$ 634	$ 677	$ 562
Weighted average shares outstanding – Basic
Common stock - basic (in shares)	2,542	2,542	2,542
Weighted average shares outstanding – Diluted
Common stock - diluted (in shares)	2,542	2,542	2,542