Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 119,837	$ 203,693
Total fixed maturities, available-for-sale, Amortized Cost	5,657,808	5,599,111
Total fixed-maturities available for sale, Fair Value	5,209,025	5,188,228
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Total	5,774,322	5,734,767
Total fixed maturities, available-for-sale, Amortized Cost	5,657,808	5,599,111
Gross Unrealized Gains	18,967	24,174
Gross Unrealized Losses	(478,295)	(443,531)
Fair Value	5,314,994	5,315,410
Total fixed-maturities available for sale, Fair Value	5,209,025	5,188,228
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Total	167,869	171,194
Gross Unrealized Gains	0	93
Gross Unrealized Losses	(30,011)	(26,891)
Fair Value	137,858	144,396
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Total	172,084	158,539
Gross Unrealized Gains	218	283
Gross Unrealized Losses	(15,537)	(16,037)
Fair Value	156,765	142,785
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Total	2,886,238	2,876,175
Gross Unrealized Gains	7,042	12,286
Gross Unrealized Losses	(283,575)	(259,177)
Fair Value	2,609,705	2,629,284
RMBS
Debt Securities, Available-for-sale [Line Items]
Total	1,138,990	1,089,919
Gross Unrealized Gains	8,842	8,250
Gross Unrealized Losses	(98,359)	(84,098)
Fair Value	1,049,473	1,014,071
CMBS
Debt Securities, Available-for-sale [Line Items]
Total	565,949	605,029
Gross Unrealized Gains	55	51
Gross Unrealized Losses	(42,424)	(46,697)
Fair Value	523,580	558,383
CLO
Debt Securities, Available-for-sale [Line Items]
Total	475,769	494,339
Gross Unrealized Gains	188	63
Gross Unrealized Losses	(4,347)	(6,553)
Fair Value	471,610	487,849
Other ABS
Debt Securities, Available-for-sale [Line Items]
Total	321,559	286,988
Gross Unrealized Gains	1,084	1,608
Gross Unrealized Losses	(4,042)	(4,037)
Fair Value	318,601	284,559
Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Total		5,128
Gross Unrealized Gains		0
Gross Unrealized Losses		(41)
Fair Value		5,087
Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Total	45,864	47,456
Gross Unrealized Gains	1,538	1,540
Gross Unrealized Losses	0	0
Fair Value	47,402	48,996
Loaned securities, amortized cost | Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	116,514	135,656
Loaned securities, fair value | Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 105,969	$ 127,182