Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, amortized cost	$ 455,586
Due after one year through five years, amortized cost	1,224,123
Due after five years through ten years, amortized cost	1,568,950
Due after ten years, amortized cost	4,364,023
Amortized cost, sub-total	7,612,682
Total fixed maturities, amortized cost	9,669,656	$ 9,591,734
Due in one year or less, estimated fair value	457,635
Due after one year through five years, estimated fair value	1,267,114
Due after five years through ten years, estimated fair value	1,645,516
Due after ten years, estimated fair value	4,613,256
Estimated fair value, sub-total	7,983,521
Total fixed maturities, estimated fair value	10,053,492	$ 9,891,510
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	1,188,439
Fixed maturities, estimated fair value	1,183,399
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	830,679
Fixed maturities, estimated fair value	848,775
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	37,856
Fixed maturities, estimated fair value	$ 37,797