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

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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