Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, amortized cost	$ 375,471
Due after one year through five years, amortized cost	1,232,430
Due after five years through ten years, amortized cost	1,567,938
Due after ten years, amortized cost	4,323,766
Amortized cost, sub-total	7,499,605
Total fixed maturities, amortized cost	9,515,082	$ 9,591,734
Due in one year or less, estimated fair value	377,672
Due after one year through five years, estimated fair value	1,276,160
Due after five years through ten years, estimated fair value	1,646,296
Due after ten years, estimated fair value	4,591,590
Estimated fair value, sub-total	7,891,718
Total fixed maturities, estimated fair value	9,919,346	$ 9,891,510
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	1,195,384
Fixed maturities, estimated fair value	1,191,410
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	799,872
Fixed maturities, estimated fair value	816,062
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	20,221
Fixed maturities, estimated fair value	$ 20,156