Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,732,454
Loaned securities	130,369	$ 112,139
Total fixed maturities, available-for-sale, Amortized Cost	5,655,280	5,587,261
Fair Value	5,242,487
Total fixed-maturities available for sale, Fair Value	5,172,375	5,017,711
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, available-for-sale, Amortized Cost	5,655,280	5,587,261
Total fixed-maturities available for sale, Fair Value	5,172,375	5,017,711
Loaned securities, amortized cost
Debt Securities, Available-for-sale [Line Items]
Loaned securities	77,174
Loaned securities, fair value
Debt Securities, Available-for-sale [Line Items]
Loaned securities	70,112
Fixed-maturities available for sale \| U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	191,827	174,138
Gross Unrealized Gains	713	206
Gross Unrealized Losses	(24,369)	(28,902)
Fair Value	168,171	145,442
Fixed-maturities available for sale \| State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	182,415	164,325
Gross Unrealized Gains	478	0
Gross Unrealized Losses	(16,471)	(21,939)
Fair Value	166,422	142,386
Fixed-maturities available for sale \| Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,901,464	2,886,905
Gross Unrealized Gains	3,882	1,403
Gross Unrealized Losses	(303,775)	(350,537)
Fair Value	2,601,571	2,537,771
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,043,417	1,025,795
Gross Unrealized Gains	1,776	1,163
Gross Unrealized Losses	(82,724)	(98,559)
Fair Value	962,469	928,399
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	637,554	645,890
Gross Unrealized Gains	3	13
Gross Unrealized Losses	(47,719)	(52,546)
Fair Value	589,838	593,357
Fixed-maturities available for sale \| CLO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	506,227	518,677
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(17,445)	(20,485)
Fair Value	488,784	498,192
Fixed-maturities available for sale \| Other ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	203,111	168,033
Gross Unrealized Gains	615	69
Gross Unrealized Losses	(4,967)	(6,743)
Fair Value	198,759	161,359
Fixed-maturities available for sale \| Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,121	5,118
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(107)	(143)
Fair Value	5,014	4,975
Fixed-maturities available for sale \| Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	61,318	54,578
Gross Unrealized Gains	194	80
Gross Unrealized Losses	(53)	(1,639)
Fair Value	61,459	53,019
Fixed-maturities available for sale \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,732,454	5,643,459
Gross Unrealized Gains	7,663	2,934
Gross Unrealized Losses	(497,630)	(581,493)
Fair Value	5,242,487	5,064,900
Fixed-maturities available for sale \| Loaned securities, amortized cost \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	77,174	56,198
Fixed-maturities available for sale \| Loaned securities, fair value \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 70,112	$ 47,189

Available-For-Sale Debt Securities, Amortized Cost Basis, Including Loaned Securities

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Available-for-sale Securities, Debt Securities, Including Loaned Securities

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of asset associated with securities loaned to entities in exchange for collateral.

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