Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,737,089
Loaned securities	89,919	$ 112,139
Total fixed maturities, available-for-sale, Amortized Cost	5,685,122	5,587,261
Fair Value	5,200,219
Total fixed-maturities available for sale, Fair Value	5,155,897	5,017,711
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, available-for-sale, Amortized Cost	5,685,122	5,587,261
Total fixed-maturities available for sale, Fair Value	5,155,897	5,017,711
Loaned securities, amortized cost
Debt Securities, Available-for-sale [Line Items]
Loaned securities	51,967
Loaned securities, fair value
Debt Securities, Available-for-sale [Line Items]
Loaned securities	44,322
Fixed-maturities available for sale \| U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	171,925	174,138
Gross Unrealized Gains	306	206
Gross Unrealized Losses	(26,423)	(28,902)
Fair Value	145,808	145,442
Fixed-maturities available for sale \| State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	179,911	164,325
Gross Unrealized Gains	203	0
Gross Unrealized Losses	(16,875)	(21,939)
Fair Value	163,239	142,386
Fixed-maturities available for sale \| Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,870,466	2,886,905
Gross Unrealized Gains	2,130	1,403
Gross Unrealized Losses	(325,497)	(350,537)
Fair Value	2,547,099	2,537,771
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,082,114	1,025,795
Gross Unrealized Gains	3,328	1,163
Gross Unrealized Losses	(95,185)	(98,559)
Fair Value	990,257	928,399
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	632,524	645,890
Gross Unrealized Gains	18	13
Gross Unrealized Losses	(58,786)	(52,546)
Fair Value	573,756	593,357
Fixed-maturities available for sale \| CLO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	504,216	518,677
Gross Unrealized Gains	61	0
Gross Unrealized Losses	(15,862)	(20,485)
Fair Value	488,415	498,192
Fixed-maturities available for sale \| Other ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	241,398	168,033
Gross Unrealized Gains	143	69
Gross Unrealized Losses	(5,623)	(6,743)
Fair Value	235,918	161,359
Fixed-maturities available for sale \| Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,123	5,118
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(106)	(143)
Fair Value	5,017	4,975
Fixed-maturities available for sale \| Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49,412	54,578
Gross Unrealized Gains	1,298	80
Gross Unrealized Losses	0	(1,639)
Fair Value	50,710	53,019
Fixed-maturities available for sale \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,737,089	5,643,459
Gross Unrealized Gains	7,487	2,934
Gross Unrealized Losses	(544,357)	(581,493)
Fair Value	5,200,219	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	51,967	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	$ 44,322	$ 47,189

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