Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 297,751	$ 341,862
Adjustments to reconcile net income to net cash provided by operating activities:
Decrease (increase) in premiums receivable	(14,203)	(105,460)
Decrease (increase) in funds held by reinsureds, net	(67,033)	(25,584)
Decrease (increase) in reinsurance recoverables	(125,881)	(14,518)
Decrease (increase) in income taxes	1,251	24,908
Decrease (increase) in prepaid reinsurance premiums	(7,167)	(27,071)
Increase (decrease) in reserve for losses and loss adjustment expenses	632,398	655,070
Increase (decrease) in future policy benefit reserve	(1,146)	(162)
Increase (decrease) in unearned premiums	4,045	196,631
Increase (decrease) in other net payable to reinsurers	46,310	105,390
Increase (decrease) in losses in course of payment	(125,074)	11,980
Change in equity adjustments in limited partnerships	(97,831)	(116,767)
Distribution of limited partnership income	71,174	18,125
Change in other assets and liabilities, net	47,052	(149,480)
Non-cash compensation expense	11,912	11,021
Amortization of bond premium (accrual of bond discount)	19,254	17,323
Net (gains) losses on investments	153,627	(38,902)
Net cash provided by (used in) operating activities	846,439	904,366
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from fixed maturities matured/called - available for sale, at market value	849,019	818,352
Proceeds from fixed maturities sold - available for sale, at market value	418,988	228,278
Proceeds from equity securities sold, at fair value	90,101	281,313
Distributions from other invested assets	162,719	52,211
Cost of fixed maturities acquired - available for sale, at market value	(2,010,859)	(1,776,730)
Cost of equity securities acquired, at fair value	(195,026)	(174,981)
Cost of other invested assets acquired	(137,430)	(98,939)
Net change in short-term investments	354,761	308,585
Net change in unsettled securities transactions	46,399	(93,610)
Net cash provided by (used in) investing activities	(421,328)	(455,521)
CASH FLOWS FROM FINANCING ACTIVITIES:
Common shares issued during the period for share-based compensation, net of expense	(14,450)	(10,583)
Purchase of treasury shares	(1,322)	(23,545)
Dividends paid to shareholders	(61,097)	(62,229)
Cost of shares withheld on settlements of share-based compensation awards	(16,692)	(12,507)
Net cash provided by (used in) financing activities	(93,561)	(108,864)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	5,807	(8,972)
Net increase (decrease) in cash	337,357	331,009
Cash, beginning of period	1,440,861	801,651
Cash, end of period	1,778,218	1,132,660
SUPPLEMENTAL CASH FLOW INFORMATION:
Income taxes paid (recovered)	2,681	6,417
Interest paid	$ 2,210	$ 1,880