Other Comprehensive Income (Loss) (Reclassifications From Accumulated Other Comprehensive Income (Loss) Into Income, By Component) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains (losses)	$ 681	$ (946)
Total before taxes	732,676	42,837
Underwriting, acquisition and insurance expenses	(455,212)	(424,390)
Income taxes	(155,163)	(108,431)
Net income (loss)	577,513	(65,594)
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 gains (losses)	312	(1,031)
Income taxes	(66)	217
Net income (loss)	246	(814)
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	(1,723)	(800)
Income taxes	362	136
Net income (loss)	$ (1,361)	$ (664)