Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net (losses) earnings	$ (185,012)	$ 752,735
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	73,417	56,942
Change in the fair value of equity securities	280,790	(536,013)
Net realized capital (gains) losses	25,074	(16,796)
Change in allowance for credit losses on available for sale securities	14,354
Change in allowance for credit losses on available for sale securities		10,020
(Increase) decrease in reinsurance recoverables, net of reinsurance payable	154,221	271,113
(Increase) decrease in premium balances receivable	(141,471)	(122,872)
(Increase) decrease in ceded unearned premiums	(43,700)	(22,084)
(Increase) decrease in deferred acquisition costs	(29,407)	(38,099)
(Increase) decrease in funds held under reinsurance agreements	(769)	14,471
Increase (decrease) in unearned premiums	206,891	197,072
Increase (decrease) in loss and loss adjustment expenses	122,975	(618,496)
Change in unrealized foreign currency exchange rate losses (gains)	53,465	(6,370)
Other, net	(221,491)	231,955
Net adjustments	494,349	(579,157)
Net cash provided by (used in) operating activities	309,337	173,578
Cash flows from investing activities
Purchases of debt securities	(3,813,237)	(4,197,740)
Purchases of equity securities	(605,415)	(134,894)
Sales of debt securities	2,380,250	1,876,234
Maturities and redemptions of debt securities	788,886	443,555
Sales of equity securities	1,391,193	1,950,478
Net (purchases) sales of short-term investments	(197,843)	(156,700)
Net (purchases) sales and maturities of commercial mortgage loans	(794)	(14,905)
(Purchases) sales of property and equipment	(17,784)	(23,942)
Purchases of affiliates and subsidiaries, net of cash acquired	(123,939)	(64,084)
Other, net	470,018	8,842
Net cash provided by (used in) investing activities	271,335	(313,156)
Cash flows from financing activities
Repayment of senior notes	(307,095)
Treasury stock acquisitions	(44,268)	(93,152)
Proceeds from issuance of senior notes	499,335
Debt issue costs paid	(4,550)
Increase (decrease) in other debt	(32,171)	46,006
Cash dividends paid	(215,013)
Other, net	1,898	(31,344)
Net cash provided by (used in) financing activities	(101,864)	(78,490)
Effect of foreign exchange rate changes on cash	(5,235)	4,123
Net increase (decrease) in cash	473,573	(213,945)
Cash at beginning of period	1,179,098	1,038,763
Cash at end of period	1,652,671	824,818
Supplemental disclosures of cash flow information
Interest paid	45,430	48,203
Income taxes paid (refund received)	$ 38,222	$ (20,672)