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, 2022	Dec. 31, 2021
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 285,391	$ 487,712
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	10,219	4,026
Available-for-sale Securities, 12 Months or Greater, Fair Value	453,520	17,021
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	58,939	268
Available-for-sale Securities, Fair Value	738,911	504,733
Available For Sale Securities, Gross Unrealized Losses	69,158	4,294
State and municipal
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,720,443	502,333
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	89,272	7,403
Available-for-sale Securities, 12 Months or Greater, Fair Value	598,797	29,547
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	79,320	2,156
Available-for-sale Securities, Fair Value	2,319,240	531,880
Available For Sale Securities, Gross Unrealized Losses	168,592	9,559
Mortgage- Backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,099,549	558,751
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	75,430	6,900
Available-for-sale Securities, 12 Months or Greater, Fair Value	473,318	106,130
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	115,528	4,762
Available-for-sale Securities, Fair Value	1,572,867	664,881
Available For Sale Securities, Gross Unrealized Losses	190,958	11,662
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,569,647	3,832,944
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	48,390	18,503
Available-for-sale Securities, 12 Months or Greater, Fair Value	2,176,638	75,385
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	103,932	291
Available-for-sale Securities, Fair Value	3,746,285	3,908,329
Available For Sale Securities, Gross Unrealized Losses	152,322	18,794
Corporate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	3,690,856	2,582,860
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	150,115	29,322
Available-for-sale Securities, 12 Months or Greater, Fair Value	2,349,281	51,095
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	256,631	3,088
Available-for-sale Securities, Fair Value	6,040,137	2,633,955
Available For Sale Securities, Gross Unrealized Losses	406,746	32,410
Foreign government
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	477,672	758,975
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	29,815	15,793
Available-for-sale Securities, 12 Months or Greater, Fair Value	711,786	82,057
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	105,243	31,701
Available-for-sale Securities, Fair Value	1,189,458	841,032
Available For Sale Securities, Gross Unrealized Losses	135,058	47,494
Debt Securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	8,843,558	8,723,575
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	403,241	81,947
Available-for-sale Securities, 12 Months or Greater, Fair Value	6,763,340	361,235
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	719,593	42,266
Available-for-sale Securities, Fair Value	15,606,898	9,084,810
Available For Sale Securities, Gross Unrealized Losses	$ 1,122,834	$ 124,213