Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	$ 95,286	$ 103,996
Total fixed-maturities available for sale	5,563,766	5,367,729
Total fixed-maturities available for sale	5,401,704	5,517,078
Fixed-maturities available for sale \| U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	200,188	221,407
Gross Unrealized Gains	97	1,719
Gross Unrealized Losses	(10,095)	(1,396)
Fair Value	190,190	221,730
Fixed-maturities available for sale \| State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	163,188	162,964
Gross Unrealized Gains	4,010	14,694
Gross Unrealized Losses	(5,806)	(401)
Fair Value	161,392	177,257
Fixed-maturities available for sale \| Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,992,078	2,867,063
Gross Unrealized Gains	31,307	133,665
Gross Unrealized Losses	(132,705)	(24,886)
Fair Value	2,890,680	2,975,842
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	818,893	697,581
Gross Unrealized Gains	2,141	14,313
Gross Unrealized Losses	(32,875)	(6,777)
Fair Value	788,159	705,117
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	674,217	690,827
Gross Unrealized Gains	1,074	21,444
Gross Unrealized Losses	(14,595)	(3,068)
Fair Value	660,696	709,203
Fixed-maturities available for sale \| CLO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	524,328	529,906
Gross Unrealized Gains	419	1,032
Gross Unrealized Losses	(4,664)	(898)
Fair Value	520,083	530,040
Fixed-maturities available for sale \| Other ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	185,896	210,657
Gross Unrealized Gains	376	1,142
Gross Unrealized Losses	(2,594)	(612)
Fair Value	183,678	211,187
Fixed-maturities available for sale \| Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,111	5,109
Gross Unrealized Gains	4	187
Gross Unrealized Losses	0	0
Fair Value	5,115	5,296
Fixed-maturities available for sale \| Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	60,441	45,384
Gross Unrealized Gains	0	1,633
Gross Unrealized Losses	(416)	0
Fair Value	60,025	47,017
Fixed-maturities available for sale \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,624,340	5,430,898
Total fixed-maturities available for sale	5,563,766	5,367,729
Gross Unrealized Gains	39,428	189,829
Gross Unrealized Losses	(203,750)	(38,038)
Fair Value	5,460,018	5,582,689
Total fixed-maturities available for sale	5,401,704	5,517,078
Fixed-maturities available for sale \| Loaned securities, amortized cost \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	60,574	63,169
Fixed-maturities available for sale \| Loaned securities, fair value \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	$ 58,314	$ 65,611

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 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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