Segment Reporting (Schedule Of Underwriting Results For Operating Segments To Income (Loss) Before Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss)	$ (114,606)	$ (27,539)	$ (35,071)	$ 365,035
Net investment income	234,233	181,058	420,116	501,062
Net realized capital gains (losses)	110,203	(12,943)	84,263	109,561
Net derivative gain (loss)	2,456	(189)	(1,048)	3,395
Corporate expenses	(10,618)	(8,435)	(29,184)	(22,622)
Interest, fee and bond issue cost amortization expense	(6,641)	(7,907)	(21,477)	(23,972)
Other income (expense)	57,481	(31,025)	48,354	(52,550)
INCOME (LOSS) BEFORE TAXES	$ 272,508	$ 93,020	$ 465,953	$ 879,909