Investments (Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fixed maturity securities:
Due in one year or less	$ 200,963
Due after one year through five years	532,344
Due after five years through ten years	286,031
Due after ten years	1,873,439
Total	$ 2,892,777	$ 2,814,553
External credit rating, non investment grade [Member]
Credit Derivatives [Line Items]
Percentage of fixed maturities	3.40%