Consolidated Statements Of Operations And Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REVENUES:
Premiums earned	$ 5,489,035	$ 4,839,058	$ 1,949,595
Net investment income	356,211	314,381	286,259
Net realized capital gains (losses):
Other-than-temporary impairments on fixed maturity securities	(19,643)	(6,164)	(6,077)
Other-than-temporary impairments on fixed maturity securities transferred to other comprehensive income (loss)
Other net realized capital gains (losses)	439,010	(179,192)	167,630
Total net realized capital gains (losses)	419,367	(185,356)	161,553
Other income (expense)	(1,589)	(9,568)	25,866
Total revenues	6,263,024	4,958,515	2,423,273
CLAIMS AND EXPENSES:
Incurred losses and loss adjustment expenses	3,829,122	4,811,018	2,039,751
Commission, brokerage, taxes and fees	1,270,053	1,141,714	210,925
Other underwriting expenses	350,901	293,347	254,886
Corporate expenses	13,063	11,034	7,394
Interest, fee and bond issue cost amortization expense	34,931	30,611	31,183
Total claims and expenses	5,498,070	6,287,724	2,544,139
INCOME (LOSS) BEFORE TAXES	764,955	(1,329,209)	(120,866)
Income tax expense (benefit)	135,228	(367,025)	(200,736)
NET INCOME (LOSS)	629,727	(962,184)	79,870
Other comprehensive income (loss), net of tax :
Unrealized appreciation (depreciation) ("URA(D)") on securities arising during the period	175,482	(92,966)	(10,536)
Less: reclassification adjustment for realized losses (gains) included in net income (loss)	5,080	2,021	2,303
Total URA(D) on securities arising during the period	180,562	(90,945)	(8,233)
Foreign currency translation adjustments	17,153	(36,431)	37,427
Benefit plan actuarial net gain (loss) for the period	(12,591)	(510)	1,027
Reclassification adjustment for amortization of net (gain) loss included in net income (loss)	5,453	5,021	5,477
Total benefit plan net gain (loss) for the period	(7,138)	4,511	6,504
Total other comprehensive income (loss), net of tax	190,577	(122,865)	35,698
COMPREHENSIVE INCOME (LOSS)	$ 820,304	$ (1,085,049)	$ 115,568