Segment Reporting (Schedule Of Underwriting Results For Operating Segments To Income (Loss) Before Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss)	$ 50,943	$ 196,886	$ 79,535	$ 392,574
Net investment income	38,083	179,028	185,883	320,004
Net realized capital gains (losses)	184,648	30,272	(25,940)	122,504
Net derivative gain (loss)	11,869	353	(3,504)	3,584
Corporate expenses	(8,733)	(7,535)	(18,566)	(14,187)
Interest, fee and bond issue cost amortization expense	(7,253)	(8,434)	(14,836)	(16,065)
Other income (expense)	(32,490)	(18,225)	(9,127)	(21,525)
INCOME (LOSS) BEFORE TAXES	$ 237,067	$ 372,345	$ 193,445	$ 786,889