Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	$ 141,614	$ 203,693
Total fixed maturities, available-for-sale, Amortized Cost	5,583,574	5,599,111
Total fixed-maturities available for sale, Fair Value	5,292,480	5,188,228
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Total	5,710,955	5,734,767
Total fixed maturities, available-for-sale, Amortized Cost	5,583,574	5,599,111
Gross Unrealized Gains	49,612	24,174
Gross Unrealized Losses	(345,148)	(443,531)
Fair Value	5,415,419	5,315,410
Total fixed-maturities available for sale, Fair Value	5,292,480	5,188,228
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Total	160,871	171,194
Gross Unrealized Gains	25	93
Gross Unrealized Losses	(24,634)	(26,891)
Fair Value	136,262	144,396
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Total	172,140	158,539
Gross Unrealized Gains	645	283
Gross Unrealized Losses	(12,483)	(16,037)
Fair Value	160,302	142,785
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Total	2,858,351	2,876,175
Gross Unrealized Gains	26,816	12,286
Gross Unrealized Losses	(210,302)	(259,177)
Fair Value	2,674,865	2,629,284
RMBS
Debt Securities, Available-for-sale [Line Items]
Total	1,111,244	1,089,919
Gross Unrealized Gains	14,870	8,250
Gross Unrealized Losses	(67,660)	(84,098)
Fair Value	1,058,454	1,014,071
CMBS
Debt Securities, Available-for-sale [Line Items]
Total	499,415	605,029
Gross Unrealized Gains	117	51
Gross Unrealized Losses	(26,220)	(46,697)
Fair Value	473,312	558,383
CLO
Debt Securities, Available-for-sale [Line Items]
Total	469,209	494,339
Gross Unrealized Gains	383	63
Gross Unrealized Losses	(1,831)	(6,553)
Fair Value	467,761	487,849
Other ABS
Debt Securities, Available-for-sale [Line Items]
Total	394,154	286,988
Gross Unrealized Gains	4,673	1,608
Gross Unrealized Losses	(2,018)	(4,037)
Fair Value	396,809	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	45,571	47,456
Gross Unrealized Gains	2,083	1,540
Gross Unrealized Losses	0	0
Fair Value	47,654	48,996
Loaned securities, amortized cost | Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	127,381	135,656
Loaned securities, fair value | Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	$ 122,939	$ 127,182