Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 405,074
Due after one year through five years, amortized cost	1,297,910
Due after five years through ten years, amortized cost	2,140,339
Due after ten years, amortized cost	3,426,491
Amortized cost, sub-total	7,269,814
Total fixed maturities, amortized cost	9,852,710	$ 9,950,773
Due in one year or less, estimated fair value	403,559
Due after one year through five years, estimated fair value	1,316,382
Due after five years through ten years, estimated fair value	2,221,684
Due after ten years, estimated fair value	3,634,217
Estimated fair value, sub-total	7,575,842
Total fixed maturities, estimated fair value	10,162,419	10,043,188
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	1,690,466
Total fixed maturities, amortized cost	1,690,466	1,691,572
Fixed maturities, estimated fair value	1,683,611
Total fixed maturities, estimated fair value	1,683,611	1,650,199
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	879,245
Total fixed maturities, amortized cost	879,245	886,501
Fixed maturities, estimated fair value	889,877
Total fixed maturities, estimated fair value	889,877	880,172
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	13,185
Total fixed maturities, amortized cost	13,185	19,614
Fixed maturities, estimated fair value	13,089
Total fixed maturities, estimated fair value	$ 13,089	$ 19,408