STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating revenue
Operating revenue	$ 621,458	$ 448,564	$ 1,193,618	$ 847,880
Operating expenses
Operating expenses	526,135	365,116	1,020,728	697,492
Operating income	95,323	83,448	172,890	150,388
Investment income
Net investment income	7,104	6,239	13,924	12,220
Net realized investment (losses) gains	(32)	124	(497)	640
Net impairment losses recognized in earnings	(646)	(61)	(646)	(182)
Equity in (losses) earnings of limited partnerships	(219)	149	(411)	362
Total investment income	6,207	6,451	12,370	13,040
Interest expense, net	602	257	1,155	423
Other income (expense)	58	(407)	102	(816)
Income before income taxes	100,986	89,235	184,207	162,189
Income tax expense	21,280	30,708	38,743	55,786
Net income	$ 79,706	$ 58,527	$ 145,464	$ 106,403
Class A
Net income per share
Common stock - basic (in dollars per share)	$ 1.71	$ 1.26	$ 3.12	$ 2.28
Common stock - diluted (in dollars per share)	$ 1.52	$ 1.12	$ 2.78	$ 2.03
Weighted average shares outstanding – Basic
Common stock - basic (in shares)	46,188,705	46,180,852	46,188,309	46,184,666
Weighted average shares outstanding – Diluted
Common stock - diluted (in shares)	52,312,849	52,299,395	52,311,741	52,355,214
Dividends declared per share
Common stock (in dollars per share)	$ 0.8400	$ 0.7825	$ 1.6800	$ 1.5650
Class B
Net income per share
Common stock - basic (in dollars per share)	257	189	469	343
Common stock - diluted (in dollars per share)	$ 257	$ 188	$ 468	$ 343
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	$ 252.000	$ 234.750
Management fee revenue, policy issuance and renewal services [Member]
Operating revenue
Operating revenue	$ 454,572	$ 441,319	$ 860,550	$ 833,377
Operating expenses
Operating expenses	379,628	365,116	728,258	697,492
Management fee revenue, administrative services [Member]
Operating revenue
Operating revenue	13,299		26,373
Administrative services reimbursements [Member]
Operating revenue
Operating revenue	146,507		292,470
Operating expenses
Operating expenses	146,507		292,470
Service agreement revenue [Member]
Operating revenue
Operating revenue	$ 7,080	$ 7,245	$ 14,225	$ 14,503