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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
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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

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