Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 337,917
Due after one year through five years, amortized cost	1,256,079
Due after five years through ten years, amortized cost	2,157,624
Due after ten years, amortized cost	3,068,760
Amortized cost, sub-total	6,820,380
Fixed maturities, amortized cost	9,448,840	$ 9,950,773
Due in one year or less, estimated fair value	333,759
Due after one year through five years, estimated fair value	1,289,760
Due after five years through ten years, estimated fair value	2,274,569
Due after ten years, estimated fair value	3,355,855
Estimated fair value, sub-total	7,253,943
Available-for-sale fixed maturity investments, estimated fair value	9,970,909	10,043,188
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	1,761,777
Fixed maturities, amortized cost	1,761,777	1,691,572
Estimated fair value	1,817,845
Available-for-sale fixed maturity investments, estimated fair value	1,817,845	1,650,199
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	855,641
Fixed maturities, amortized cost	855,641	886,501
Estimated fair value	888,073
Available-for-sale fixed maturity investments, estimated fair value	888,073	880,172
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	11,042
Fixed maturities, amortized cost	11,042	19,614
Estimated fair value	11,048
Available-for-sale fixed maturity investments, estimated fair value	$ 11,048	$ 19,408