Fixed Maturity Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - External Credit Rating, Investment Grade - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 487,712	$ 47,649
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	4,026	347
Available-for-sale Securities, 12 Months or Greater, Fair Value	17,021	17
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	268	0
Available-for-sale Securities, Fair Value	504,733	47,666
Available For Sale Securities, Gross Unrealized Losses	4,294	347
State and municipal
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	502,333	147,754
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	7,403	1,165
Available-for-sale Securities, 12 Months or Greater, Fair Value	29,547	20,528
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	2,156	904
Available-for-sale Securities, Fair Value	531,880	168,282
Available For Sale Securities, Gross Unrealized Losses	9,559	2,069
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	558,751	212,388
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	6,900	5,121
Available-for-sale Securities, 12 Months or Greater, Fair Value	106,130	23,943
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	4,762	230
Available-for-sale Securities, Fair Value	664,881	236,331
Available For Sale Securities, Gross Unrealized Losses	11,662	5,351
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	3,832,944	1,389,133
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	18,503	6,563
Available-for-sale Securities, 12 Months or Greater, Fair Value	75,385	656,877
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	291	26,934
Available-for-sale Securities, Fair Value	3,908,329	2,046,010
Available For Sale Securities, Gross Unrealized Losses	18,794	33,497
Corporate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	2,582,860	612,177
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	29,322	6,721
Available-for-sale Securities, 12 Months or Greater, Fair Value	51,095	39,985
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	3,088	1,759
Available-for-sale Securities, Fair Value	2,633,955	652,162
Available For Sale Securities, Gross Unrealized Losses	32,410	8,480
Foreign government
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	758,975	143,729
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	15,793	22,871
Available-for-sale Securities, 12 Months or Greater, Fair Value	82,057	6,218
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	31,701	21,577
Available-for-sale Securities, Fair Value	841,032	149,947
Available For Sale Securities, Gross Unrealized Losses	47,494	44,448
Debt Securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	8,723,575	2,552,830
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	81,947	42,788
Available-for-sale Securities, 12 Months or Greater, Fair Value	361,235	747,568
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	42,266	51,404
Available-for-sale Securities, Fair Value	9,084,810	3,300,398
Available For Sale Securities, Gross Unrealized Losses	$ 124,213	$ 94,192