Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Document Period End Date	Sep. 30, 2019
Due in one year or less, amortized cost	$ 491,999
Due after one year through five years, amortized cost	1,285,281
Due after five years through ten years, amortized cost	2,081,192
Due after ten years, amortized cost	3,156,611
Amortized cost, sub-total	7,015,083
Total fixed maturities, amortized cost	9,601,898	$ 9,950,773
Due in one year or less, estimated fair value	485,791
Due after one year through five years, estimated fair value	1,310,381
Due after five years through ten years, estimated fair value	2,197,791
Due after ten years, estimated fair value	3,500,386
Estimated fair value, sub-total	7,494,349
Total fixed maturities, estimated fair value	10,204,025	10,043,188
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	1,708,617
Total fixed maturities, amortized cost	1,708,617	1,691,572
Fixed maturities, estimated fair value	1,790,083
Total fixed maturities, estimated fair value	1,790,083	1,650,199
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	868,317
Total fixed maturities, amortized cost	868,317	886,501
Fixed maturities, estimated fair value	909,669
Total fixed maturities, estimated fair value	909,669	880,172
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	9,881
Total fixed maturities, amortized cost	9,881	19,614
Fixed maturities, estimated fair value	9,924
Total fixed maturities, estimated fair value	$ 9,924	$ 19,408