Segment Reporting (Schedule Of Underwriting Results For Operating Segments To Income (Loss) Before Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting [Abstract]
Underwriting gain (loss)									$ 208,821	$ 294,311	$ 228,199
Net investment income	$ 67,920	$ 64,570	$ 73,872	$ 58,445	$ 66,384	$ 63,363	$ 70,925	$ 72,581	264,807	273,253	290,310
Net realized capital gains (losses)	$ 58,334	$ (50,063)	$ 29,165	$ (66,377)	$ 99,509	$ (121,695)	$ 51,225	$ 21,296	(28,941)	50,335	206,679
Corporate expense									(8,277)	(7,179)	(7,252)
Interest, fee and bond issue cost amortization expense									(35,435)	(35,434)	(37,970)
Other income (expense)									(10,542)	29,256	(22,278)
INCOME (LOSS) BEFORE TAXES									$ 390,433	$ 604,542	$ 657,688