Fixed Maturity Securities In An Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) $ in Thousands	Mar. 31, 2022 USD ($) position	Dec. 31, 2021 USD ($)
Corporate
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	$ 4,186,326	$ 2,633,955
Gross Unrealized Loss	180,531	32,410
State and municipal
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	1,455,908	531,880
Gross Unrealized Loss	60,924	9,559
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	1,210,459	664,881
Gross Unrealized Loss	64,409	11,662
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	4,085,270	3,908,329
Gross Unrealized Loss	$ 63,573	$ 18,794
Noninvestment Grade Investments at Loss Position
Debt Securities, Available-for-sale [Line Items]
Number of Securities \| position	58
Aggregate Fair Value	$ 177,782
Gross Unrealized Loss	$ 35,386
Noninvestment Grade Investments at Loss Position \| Foreign government
Debt Securities, Available-for-sale [Line Items]
Number of Securities \| position	37
Aggregate Fair Value	$ 132,306
Gross Unrealized Loss	$ 30,753
Noninvestment Grade Investments at Loss Position \| Corporate
Debt Securities, Available-for-sale [Line Items]
Number of Securities \| position	12
Aggregate Fair Value	$ 30,071
Gross Unrealized Loss	$ 3,158
Noninvestment Grade Investments at Loss Position \| State and municipal
Debt Securities, Available-for-sale [Line Items]
Number of Securities \| position	1
Aggregate Fair Value	$ 13,583
Gross Unrealized Loss	$ 1,422
Noninvestment Grade Investments at Loss Position \| Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Number of Securities \| position	7
Aggregate Fair Value	$ 1,785
Gross Unrealized Loss	$ 48
Noninvestment Grade Investments at Loss Position \| Asset-backed
Debt Securities, Available-for-sale [Line Items]
Number of Securities \| position	1
Aggregate Fair Value	$ 37
Gross Unrealized Loss	$ 5

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456

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Amount of accumulated unrealized loss on 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. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities 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. Includes beneficial interest in securitized financial asset.

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