STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating revenue
Operating revenue	$ 612,126	$ 442,492	$ 1,805,744	$ 1,290,372
Operating expenses
Operating expenses	515,431	361,253	1,536,159	1,058,745
Operating income	96,695	81,239	269,585	231,627
Investment income
Net investment income	7,659	5,982	21,583	18,202
Net realized investment gains (losses)	0	899	(497)	1,539
Net impairment losses recognized in earnings	0	0	(646)	(182)
Equity in earnings of limited partnerships	772	1,537	361	1,899
Total investment income	8,431	8,418	20,801	21,458
Interest expense, net	709	377	1,864	800
Other income (expense)	54	(415)	156	(1,231)
Income before income taxes	104,471	88,865	288,678	251,054
Income tax expense	24,025	30,322	62,768	86,108
Net income	$ 80,446	$ 58,543	$ 225,910	$ 164,946
Class A
Net income per share
Common stock - basic (in dollars per share)	$ 1.73	$ 1.26	$ 4.85	$ 3.54
Common stock - diluted (in dollars per share)	$ 1.54	$ 1.12	$ 4.32	$ 3.15
Weighted average shares outstanding – Basic
Common stock - basic (in shares)	46,188,941	46,188,949	46,188,522	46,186,109
Weighted average shares outstanding – Diluted
Common stock - diluted (in shares)	52,317,438	52,316,876	52,313,642	52,342,450
Dividends declared per share
Common stock (in dollars per share)	$ 0.8400	$ 0.7825	$ 2.5200	$ 2.3475
Class B
Net income per share
Common stock - basic (in dollars per share)	259	189	728	531
Common stock - diluted (in dollars per share)	$ 259	$ 189	$ 727	$ 531
Weighted average shares outstanding – Basic
Common stock - basic (in shares)	2,542	2,542	2,542	2,542
Weighted average shares outstanding – Diluted
Common stock - diluted (in shares)	2,542	2,542	2,542	2,542
Dividends declared per share
Common stock (in dollars per share)	$ 126.000	$ 117.375	$ 378.000	$ 352.125
Management fee revenue, policy issuance and renewal services [Member]
Operating revenue
Operating revenue	$ 451,361	$ 435,214	$ 1,311,911	$ 1,268,591
Operating expenses
Operating expenses	375,259	361,253	1,103,517	1,058,745
Management fee revenue, administrative services [Member]
Operating revenue
Operating revenue	13,521		39,894
Administrative services reimbursements [Member]
Operating revenue
Operating revenue	140,172		432,642
Operating expenses
Operating expenses	140,172		432,642
Service agreement revenue [Member]
Operating revenue
Operating revenue	$ 7,072	$ 7,278	$ 21,297	$ 21,781