Investments (Summary Of Components Of Net Realized Capital Gains (Losses)) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Other-than-temporary impairments										$ (19,643,000)	$ (6,164,000)
Total net realized capital gains (losses)	$ 157,104,000	$ 115,193,000	$ (479,360,000)	$ 256,867,000	$ 29,206,000	$ 112,542,000	$ 142,563,000	$ 135,056,000	49,804,000	419,367,000	(185,356,000)
Beginning Balance				0					0
Credit losses on securities where credit losses were not previously recorded									(22,460,000)
Increases in allowance on previously impaired securities									(6,120,000)
Decrease in allowance on previously impaired securities									2,106,000
Reduction in allowance due to disposals									24,908,000
Ending Balance	(1,566,000)				0				(1,566,000)	0
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Ending Balance	(1,566,000)								(1,566,000)
Fixed Maturity Securities [Member] | Market Value [Member]
Schedule of Available-for-sale Securities [Line Items]
Allowance for credit losses									(1,566,000)
Other-than-temporary impairments										(19,643,000)	(6,164,000)
Gains (losses) from sales									(32,614,000)	7,571,000	933,000
Fixed Maturity Securities [Member] | Fair Value [Member]
Schedule of Available-for-sale Securities [Line Items]
Gains (losses) from sales									(2,863,000)	355,000	(1,799,000)
Gains (losses) from fair value adjustments									1,944,000	1,808,000	1,506,000
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Beginning Balance
Credit losses on securities where credit losses were not previously recorded									(21,829,000)
Increases in allowance on previously impaired securities									(5,909,000)
Decrease in allowance on previously impaired securities									1,824,000
Reduction in allowance due to disposals									24,709,000
Ending Balance	(1,205,000)								(1,205,000)
Equity Securities [Member] | Fair Value [Member]
Schedule of Available-for-sale Securities [Line Items]
Gains (losses) from sales									(7,931,000)	4,144,000	(32,092,000)
Gains (losses) from fair value adjustments									276,093,000	153,728,000	(59,409,000)
Other Invested Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Gains (losses) from sales									1,705,000	6,003,000	1,815,000
Other Invested Assets [Member] | Fair Value [Member]
Schedule of Available-for-sale Securities [Line Items]
Gains (losses) from fair value adjustments									(186,102,000)	265,245,000	(90,136,000)
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gains (losses) from sales									1,138,000	156,000	$ (10,000)
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Beginning Balance
Credit losses on securities where credit losses were not previously recorded									(70,000)
Increases in allowance on previously impaired securities
Decrease in allowance on previously impaired securities
Reduction in allowance due to disposals									70,000
Ending Balance
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Beginning Balance
Credit losses on securities where credit losses were not previously recorded									(561,000)
Increases in allowance on previously impaired securities									(211,000)
Decrease in allowance on previously impaired securities									282,000
Reduction in allowance due to disposals									129,000
Ending Balance	$ (361,000)								$ (361,000)