Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Activities
Net income (loss)	$ 475,708	$ (88,674)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net realized (gains) losses	(161,007)	362,964
Equity in net (income) or loss of investment funds accounted for using the equity method and other income or loss	(135,939)	29,034
Amortization of intangible assets	14,402	16,631
Share-based compensation	40,812	28,549
Changes in:
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	560,153	506,057
Unearned premiums, net of ceded unearned premiums	560,035	392,802
Premiums receivable	(608,250)	(418,457)
Deferred acquisition costs	(126,701)	(75,135)
Reinsurance balances payable	240,206	79,807
Other items, net	(96,574)	(223,124)
Net cash provided by (used for) operating activities	762,845	610,454
Investing Activities
Purchases of fixed maturity investments	(11,530,968)	(11,965,995)
Purchases of equity securities	(309,419)	(760,683)
Purchases of other investments	(430,961)	(228,471)
Proceeds from sales of fixed maturity investments	10,917,134	11,723,123
Proceeds from sales of equity securities	284,986	266,301
Proceeds from sales, redemptions and maturities of other investments	323,591	216,131
Proceeds from redemptions and maturities of fixed maturity investments	421,042	198,356
Net settlements of derivative instruments	47,660	195,488
Net (purchases) sales of short-term investments	589,175	(11,777)
Change in cash collateral related to securities lending	0	55,001
Purchase of operating affiliate	(546,349)	0
Purchases of fixed assets	(12,490)	(8,470)
Other	(246,590)	42,500
Net cash provided by (used for) investing activities	(493,189)	(278,496)
Financing Activities
Purchases of common shares under share repurchase program	(179,266)	(75,486)
Proceeds from common shares issued, net	(10,008)	(4,527)
Proceeds from borrowings	0	16,300
Change in cash collateral related to securities lending	0	(55,001)
Third party investment in non-redeemable noncontrolling interests	15,971	(2,867)
Dividends paid to redeemable noncontrolling interests	(948)	(1,181)
Other	(1,948)	(1,331)
Preferred dividends paid	(10,403)	(10,403)
Net cash provided by (used for) financing activities	(186,602)	(134,496)
Effects of exchange rate changes on foreign currency cash and restricted cash	(6,084)	(30,723)
Increase (decrease) in cash and restricted cash	76,970	166,739
Cash and restricted cash, beginning of year	1,290,544	903,698
Cash and restricted cash, end of period	$ 1,367,514	$ 1,070,437