Fair Value Option (Gains And Losses Due To Changes In Fair Value Of Investments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Gains (losses) due to changes in fair value of investments	$ (58,532)	$ 21,857
Note Receivable [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Gains (losses) due to changes in fair value of investments	(41)	0
Investments [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Gains (losses) due to changes in fair value of investments	(58,491)	21,857
Fixed maturity securities [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Gains (losses) due to changes in fair value of investments	(46,213)	10,288
Equity Securities [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Gains (losses) due to changes in fair value of investments	(11,886)	11,541
Short-term investments [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Gains (losses) due to changes in fair value of investments	$ (392)	$ 28