Investments (Summary Of Changes In Net Unrealized Appreciation (Depreciation) For The Company's Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Change in unrealized appreciation (depreciation), pre-tax	$ (108,789)	$ 55,587	$ (344,370)	$ 392,640
Deferred tax benefit (expense)	7,380	(3,560)	36,441	(44,116)
Total URA(D) on securities arising during the period	(101,409)	52,027	(307,929)	348,524
Fixed Maturity Securities and Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Change in unrealized appreciation (depreciation), pre-tax	$ (108,789)	$ 55,587	$ (344,370)	$ 392,640