Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 203,693	$ 112,139
Total fixed-maturities, available for sale, Amortized Cost	5,599,111	5,587,261
Total fixed-maturities available for sale, Fair Value	5,188,228	5,017,711
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	171,194	174,138
Gross Unrealized Gains	93	206
Gross Unrealized Losses	(26,891)	(28,902)
Fair Value	144,396	145,442
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	158,539	164,325
Gross Unrealized Gains	283	0
Gross Unrealized Losses	(16,037)	(21,939)
Fair Value	142,785	142,386
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,876,175	2,886,905
Gross Unrealized Gains	12,286	1,403
Gross Unrealized Losses	(259,177)	(350,537)
Fair Value	2,629,284	2,537,771
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,089,919	1,025,795
Gross Unrealized Gains	8,250	1,163
Gross Unrealized Losses	(84,098)	(98,559)
Fair Value	1,014,071	928,399
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	605,029	645,890
Gross Unrealized Gains	51	13
Gross Unrealized Losses	(46,697)	(52,546)
Fair Value	558,383	593,357
CLO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	494,339	518,677
Gross Unrealized Gains	63	0
Gross Unrealized Losses	(6,553)	(20,485)
Fair Value	487,849	498,192
Other ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	286,988	168,033
Gross Unrealized Gains	1,608	69
Gross Unrealized Losses	(4,037)	(6,743)
Fair Value	284,559	161,359
Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,128	5,118
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(41)	(143)
Fair Value	5,087	4,975
Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	47,456	54,578
Gross Unrealized Gains	1,540	80
Gross Unrealized Losses	0	(1,639)
Fair Value	48,996	53,019
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,734,767	5,643,459
Total fixed-maturities, available for sale, Amortized Cost	5,599,111	5,587,261
Gross Unrealized Gains	24,174	2,934
Gross Unrealized Losses	(443,531)	(581,493)
Fair Value	5,315,410	5,064,900
Total fixed-maturities available for sale, Fair Value	5,188,228	5,017,711
Loaned securities, amortized cost | Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	135,656	56,198
Loaned securities
Debt Securities, Available-for-sale [Line Items]
Loaned securities	127,000
Loaned securities | Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 127,182	$ 47,189