Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized Cost
Due in one year or less	$ 101,546
Due after one year through five years	2,063,502
Due after five years through ten years	3,639,243
Due after ten years	5,814,572
Amortized Cost	12,737,749	$ 6,157,371
Fair Value
Due in one year or less	101,320
Due after one year through five years	2,075,819
Due after five years through ten years	3,652,143
Due after ten years	6,306,210
Fair Value	13,278,166	7,012,631
Asset-backed securities
Amortized Cost
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Amortized Cost	547,549
Fair Value
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Fair Value	547,310
Commercial mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Amortized Cost	552,653
Fair Value
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Fair Value	575,184
Residential mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Amortized Cost	18,684
Fair Value
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Fair Value	20,180
Fixed Maturities
Amortized Cost
Amortized Cost	12,737,749	6,157,371
Fair Value
Fair Value	13,278,166	7,012,631
Fixed Maturities \| Asset-backed securities
Amortized Cost
Amortized Cost	547,549	236,909
Fair Value
Fair Value	547,310	237,638
Fixed Maturities \| Commercial mortgage-backed securities
Amortized Cost
Amortized Cost	552,653	480,412
Fair Value
Fair Value	575,184	520,947
Fixed Maturities \| Residential mortgage-backed securities
Amortized Cost
Amortized Cost	18,684	49,456
Fair Value
Fair Value	$ 20,180	$ 53,235

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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