Consolidated Statements Of Operations And Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
REVENUES:
Premiums earned	$ 6,406,576	$ 5,489,035	$ 4,839,058
Net investment income	375,906	356,211	314,381
Net realized capital gains (losses):
Credit allowances on fixed maturity securities	(1,566)
Other-than-temporary impairments on fixed maturity securities		(19,643)	(6,164)
Other net realized capital gains (losses)	51,370	439,010	(179,192)
Total net realized capital gains (losses)	49,804	419,367	(185,356)
Other income (expense)	(14,579)	(1,589)	(9,568)
Total revenues	6,817,707	6,263,024	4,958,515
CLAIMS AND EXPENSES:
Incurred losses and loss adjustment expenses	4,608,144	3,829,122	4,811,018
Commission, brokerage, taxes and fees	1,373,355	1,270,053	1,141,714
Other underwriting expenses	401,033	350,901	293,347
Corporate expenses	15,985	13,063	11,034
Interest, fee and bond issue cost amortization expense	35,659	34,931	30,611
Total claims and expenses	6,434,176	5,498,070	6,287,724
INCOME (LOSS) BEFORE TAXES	383,531	764,955	(1,329,209)
Income tax expense (benefit)	31,658	135,228	(367,025)
NET INCOME (LOSS)	351,873	629,727	(962,184)
Other comprehensive income (loss), net of tax :
Unrealized appreciation (depreciation) ("URA(D)") on securities arising during the period	163,080	175,482	(92,966)
Less: reclassification adjustment for realized losses (gains) included in net income (loss)	25,468	5,080	2,021
Total URA(D) on securities arising during the period	188,548	180,562	(90,945)
Foreign currency translation adjustments	14,461	17,153	(36,431)
Benefit plan actuarial net gain (loss) for the period	(5,615)	(12,591)	(510)
Reclassification adjustment for amortization of net (gain) loss included in net income (loss)	6,300	5,453	5,021
Total benefit plan net gain (loss) for the period	685	(7,138)	4,511
Total other comprehensive income (loss), net of tax	203,694	190,577	(122,865)
COMPREHENSIVE INCOME (LOSS)	$ 555,567	$ 820,304	$ (1,085,049)