Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - Fixed Maturities - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	$ 5,052,071	$ 150,346
Less than Twelve Months, Gross Unrealized Losses	94,096	1,702
Twelve Months or More Fair Value	333,294	171,720
Twelve Months or More, Gross Unrealized Losses	19,435	9,322
Total, Fair Value	5,385,365	322,066
Total, Gross Unrealized Losses	113,531	11,024
U.S. Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	0	2,255
Less than Twelve Months, Gross Unrealized Losses	0	22
Twelve Months or More Fair Value	2,119	0
Twelve Months or More, Gross Unrealized Losses	111	0
Total, Fair Value	2,119	2,255
Total, Gross Unrealized Losses	111	22
Obligations of U.S. states and their political subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	104,621
Less than Twelve Months, Gross Unrealized Losses	701
Twelve Months or More Fair Value	0
Twelve Months or More, Gross Unrealized Losses	0
Total, Fair Value	104,621
Total, Gross Unrealized Losses	701
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	59,550	2,270
Less than Twelve Months, Gross Unrealized Losses	2,826	32
Twelve Months or More Fair Value	6,473	0
Twelve Months or More, Gross Unrealized Losses	371	0
Total, Fair Value	66,023	2,270
Total, Gross Unrealized Losses	3,197	32
U.S. public corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	1,681,201	33,295
Less than Twelve Months, Gross Unrealized Losses	23,160	341
Twelve Months or More Fair Value	180,249	2,754
Twelve Months or More, Gross Unrealized Losses	6,610	246
Total, Fair Value	1,861,450	36,049
Total, Gross Unrealized Losses	29,770	587
U.S. private corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	972,796	33,806
Less than Twelve Months, Gross Unrealized Losses	14,036	771
Twelve Months or More Fair Value	16,409	6,659
Twelve Months or More, Gross Unrealized Losses	2,844	1,427
Total, Fair Value	989,205	40,465
Total, Gross Unrealized Losses	16,880	2,198
Foreign public corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	532,445	6,432
Less than Twelve Months, Gross Unrealized Losses	8,255	97
Twelve Months or More Fair Value	29,718	6,464
Twelve Months or More, Gross Unrealized Losses	2,108	789
Total, Fair Value	562,163	12,896
Total, Gross Unrealized Losses	10,363	886
Foreign private corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	1,253,739	2,931
Less than Twelve Months, Gross Unrealized Losses	42,392	131
Twelve Months or More Fair Value	57,637	85,340
Twelve Months or More, Gross Unrealized Losses	5,616	6,657
Total, Fair Value	1,311,376	88,271
Total, Gross Unrealized Losses	48,008	6,788
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	288,971	51,914
Less than Twelve Months, Gross Unrealized Losses	1,099	183
Twelve Months or More Fair Value	0	70,503
Twelve Months or More, Gross Unrealized Losses	0	203
Total, Fair Value	288,971	122,417
Total, Gross Unrealized Losses	1,099	386
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	157,355	17,443
Less than Twelve Months, Gross Unrealized Losses	1,622	125
Twelve Months or More Fair Value	40,689	0
Twelve Months or More, Gross Unrealized Losses	1,775	0
Total, Fair Value	198,044	17,443
Total, Gross Unrealized Losses	3,397	125
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months Fair Value	1,393	0
Less than Twelve Months, Gross Unrealized Losses	5	0
Twelve Months or More Fair Value	0	0
Twelve Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	1,393	0
Total, Gross Unrealized Losses	$ 5	$ 0