Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
REVENUES:
Net premiums written	$ 7,262,437	$ 6,863,499	$ 6,433,227
Change in net unearned premiums	(331,594)	(230,211)	(61,722)
Net premiums earned	6,930,843	6,633,288	6,371,505
Net investment income	583,821	645,614	674,235
Net investment gains:
Net realized and unrealized gains on investments	73,514	120,703	160,175
Change in allowance for expected credit losses on investments	29,486	0	(5,687)
Net investment gains (losses)	103,000	120,703	154,488
Revenues from non-insurance businesses	389,888	406,541	372,985
Insurance service fees	88,777	92,680	117,757
Other income	2,596	3,370	681
Total revenues	8,098,925	7,902,196	7,691,651
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	4,468,706	4,131,116	3,974,702
Other operating costs and expenses	2,390,392	2,362,082	2,383,221
Expenses from non-insurance businesses	384,488	402,669	364,449
Interest expense	150,537	153,409	157,185
Total operating costs and expenses	7,394,123	7,049,276	6,879,557
Pre-Tax Income (Loss)	704,802	852,920	812,094
Income tax expense	(171,817)	(168,935)	(163,028)
Net income before noncontrolling interests	532,985	683,985	649,066
Noncontrolling interests	(2,315)	(2,041)	(8,317)
Net income to common stockholders	$ 530,670	$ 681,944	$ 640,749
NET INCOME PER SHARE:
Basic (dollars per share)	$ 2.84	$ 3.58	$ 3.37
Diluted (dollars per share)	$ 2.81	$ 3.52	$ 3.33