Other Comprehensive Income (Loss) (Reclassification From Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	$ (46,187)	$ (39,477)	$ 14,047	$ (99,470)
NET INCOME (LOSS)	190,880	332,868	207,492	687,419
URA(D) On Securities [Member] | Reclassification From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net realized capital gains (losses)	(6,849)	(787)	31,328	(3,523)
Income tax expense (benefit)	(408)	(1,082)	(7,186)	(168)
NET INCOME (LOSS)	(7,257)	(1,869)	24,142	(3,691)
Benefit Plan Net Gain (Loss) [Member] | Reclassification From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other underwriting expenses	2,286	1,457	3,451	2,914
Income tax expense (benefit)	(480)	(306)	(725)	(612)
NET INCOME (LOSS)	$ 1,806	$ 1,151	$ 2,726	$ 2,302