Other Comprehensive Income (Loss) (Reclassification From Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net realized capital gains (losses)	$ 30,556	$ 60,035	$ (12,806)	$ 105,452
Other underwriting expenses	(58,330)	(51,573)	(117,557)	(100,116)
Income tax expense (benefit)	(32,982)	(64,049)	(45,845)	(114,455)
NET INCOME (LOSS)	68,350	133,766	107,276	249,710
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)	(97)	21,017	39,773	56,656
Income tax expense (benefit)	34	(7,356)	(13,921)	(19,330)
NET INCOME (LOSS)	(63)	13,661	25,852	37,326
Benefit Plan Liability [Member] | Reclassification From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other underwriting expenses	2,063	2,476	4,125	4,943
Income tax expense (benefit)	(722)	(867)	(1,444)	(1,730)
NET INCOME (LOSS)	$ 1,341	$ 1,609	$ 2,681	$ 3,213