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Fixed Maturity Securities In An Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) $ in Thousands | Sep. 30, 2023 USD ($) position | Dec. 31, 2022 USD ($)
--- | --- | ---
Noninvestment Grade Investments at Loss Position |  |
Debt Securities, Available-for-sale [Line Items] |  |
Number of Securities | position | 95 |
Aggregate Fair Value | $ 151,750 |
Gross Unrealized Loss | $ 101,686 |
Foreign government | Noninvestment Grade Investments at Loss Position |  |
Debt Securities, Available-for-sale [Line Items] |  |
Number of Securities | position | 44 |
Aggregate Fair Value | $ 88,668 |
Gross Unrealized Loss | 91,468 |
Corporate |  |
Debt Securities, Available-for-sale [Line Items] |  |
Aggregate Fair Value | 6,786,931 | $ 6,040,137
Gross Unrealized Loss | $ 409,659 | 406,746
Corporate | Noninvestment Grade Investments at Loss Position |  |
Debt Securities, Available-for-sale [Line Items] |  |
Number of Securities | position | 26 |
Aggregate Fair Value | $ 35,644 |
Gross Unrealized Loss | 3,523 |
State and municipal |  |
Debt Securities, Available-for-sale [Line Items] |  |
Aggregate Fair Value | 2,374,534 | 2,319,240
Gross Unrealized Loss | $ 183,193 | 168,592
State and municipal | Noninvestment Grade Investments at Loss Position |  |
Debt Securities, Available-for-sale [Line Items] |  |
Number of Securities | position | 5 |
Aggregate Fair Value | $ 22,866 |
Gross Unrealized Loss | 6,374 |
Mortgage-backed |  |
Debt Securities, Available-for-sale [Line Items] |  |
Aggregate Fair Value | 1,985,232 | 1,572,867
Gross Unrealized Loss | $ 234,770 | 190,958
Mortgage-backed | Noninvestment Grade Investments at Loss Position |  |
Debt Securities, Available-for-sale [Line Items] |  |
Number of Securities | position | 15 |
Aggregate Fair Value | $ 4,328 |
Gross Unrealized Loss | 214 |
Asset-backed |  |
Debt Securities, Available-for-sale [Line Items] |  |
Aggregate Fair Value | 3,609,880 | 3,746,285
Gross Unrealized Loss | $ 109,025 | $ 152,322
Asset-backed | Noninvestment Grade Investments at Loss Position |  |
Debt Securities, Available-for-sale [Line Items] |  |
Number of Securities | position | 5 |
Aggregate Fair Value | $ 244 |
Gross Unrealized Loss | $ 107 |

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