Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REVENUES:
Net premiums written	$ 6,863,499	$ 6,433,227	$ 6,260,508
Change in net unearned premiums	(230,211)	(61,722)	50,911
Net premiums earned	6,633,288	6,371,505	6,311,419
Net investment income	645,614	674,235	575,788
Net realized and unrealized gains on investments:
Net realized and unrealized gains before OTTI	120,703	160,175	335,858
Other-than-temporary impairments (OTTI)	0	(5,687)	0
Net realized and unrealized gains on investments	120,703	154,488	335,858
Revenues from non-insurance businesses	406,541	372,985	326,165
Insurance service fees	92,680	117,757	134,729
Other income	3,370	681	805
Total revenues	7,902,196	7,691,651	7,684,764
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	4,131,116	3,974,702	4,002,348
Other operating costs and expenses	2,362,082	2,383,221	2,436,932
Expenses from non-insurance businesses	402,669	364,449	325,417
Interest expense	153,409	157,185	147,297
Total operating costs and expenses	7,049,276	6,879,557	6,911,994
Income before income taxes	852,920	812,094	772,770
Income tax expense	(168,935)	(163,028)	(219,433)
Net income before noncontrolling interests	683,985	649,066	553,337
Noncontrolling interests	(2,041)	(8,317)	(4,243)
Net income to common stockholders	$ 681,944	$ 640,749	$ 549,094
NET INCOME PER SHARE:
Basic (dollars per share)	$ 3.58	$ 3.37	$ 2.93
Diluted (dollars per share)	$ 3.52	$ 3.33	$ 2.84