Other Comprehensive Income (Reclassifications From Accumulated Other Comprehensive Income (Loss) Into Income, By Component) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized investment losses	$ 150	$ (496)	$ 764	$ (9,084)
Income Before Income Taxes	261,928	519,027	1,644,798	922,601
Underwriting, acquisition and insurance expenses	(475,219)	(441,961)	(1,392,747)	(1,317,921)
Income taxes	(57,975)	(109,999)	(356,849)	(299,580)
Net Income	203,953	409,028	1,287,949	623,021
Reclassification out of accumulated other comprehensive income [Member] | Unrealized holding gains on available-for-sale securities [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized investment losses	(257)	(13,383)	(962)	(6,957)
Income taxes	54	2,810	202	1,461
Net Income	(203)	(10,573)	(760)	(5,496)
Reclassification out of accumulated other comprehensive income [Member] | Net actuarial pension loss [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Underwriting, acquisition and insurance expenses	(585)	(644)	(2,960)	(2,204)
Income taxes	123	135	622	463
Net Income	$ (462)	$ (509)	$ (2,338)	$ (1,741)