Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net earnings	$ 126,883	$ 890,201	$ 54,654
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	160,002	119,513	127,374
Change in the fair value of equity securities	110,459	(709,695)	228,994
Net realized capital (gains) losses	(3,098)	6,551	3,241
Change in allowance for credit losses on available for sale securities	8,029
Change in allowance for credit losses on available for sale securities		19,660	1,328
(Increase) decrease in reinsurance recoverables, net of reinsurance payable	(79,149)	259,048	(162,499)
(Increase) decrease in premium balances receivable	(197,331)	(105,368)	(45,296)
(Increase) decrease in ceded unearned premiums	(63,745)	(26,921)	(30,980)
(Increase) decrease in deferred acquisition costs	(72,540)	(58,031)	(11,200)
(Increase) decrease in funds held under reinsurance agreements	(38,938)	(11,458)	(38,015)
Increase (decrease) in unearned premiums	417,890	299,092	84,784
Increase (decrease) in loss and loss adjustment expenses	1,042,267	(321,935)	379,044
Change in unrealized foreign currency exchange rate losses (gains)	(99,134)	(18,033)	84,089
Other, net	(274,761)	371,781	(273,095)
Net adjustments	909,951	(175,796)	347,769
Net cash provided by (used in) operating activities	1,036,834	714,405	402,423
Cash flows from investing activities
Purchases of debt securities	(6,721,073)	(6,726,809)	(4,716,070)
Purchases of equity securities	(1,974,625)	(520,961)	(1,041,887)
Sales of debt securities	4,042,915	3,645,307	3,647,156
Maturities and redemptions of debt securities	1,664,285	1,166,841	1,526,060
Sales of equity securities	1,659,234	2,296,371	1,609,647
Net (purchases) sales of short-term investments	208,263	(21,564)	(316,366)
Net (purchases) sales and maturities of commercial mortgage loans	15,967	(9,674)	(18,168)
(Purchases) sales of property and equipment	(37,519)	(47,572)	(23,286)
Purchases of affiliates and subsidiaries, net of cash acquired	(128,921)	(218,260)	(235,176)
Other, net	(12,973)	(40,218)	(86,478)
Net cash provided by (used in) investing activities	(1,284,447)	(476,539)	345,432
Cash flows from financing activities
Repayment of senior notes	(307,095)	0	0
Treasury stock acquisitions	(194,762)	(144,422)	(491,633)
Proceeds from issuance of senior notes	499,335	0	0
Debt issue costs paid	(4,550)	0	0
Increase (decrease) in other debt	85,989	81,738	104,404
Cash dividends paid	(215,013)	0	(153,967)
Other, net	(27,912)	(40,530)	4,512
Net cash provided by (used in) financing activities	(164,008)	(103,214)	(536,684)
Effect of foreign exchange rate changes on cash	23,965	5,683	(10,783)
Net (decrease) increase in cash	(387,656)	140,335	200,388
Cash at beginning of period	1,179,098	1,038,763	838,375
Cash at end of period	791,442	1,179,098	1,038,763
Supplemental disclosures of cash flow information
Interest paid	91,832	97,016	88,345
Income taxes paid (refund received)	$ 90,828	$ 61,786	$ 33,677