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INVESTMENTS - Fixed Maturities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Available for sale
Amortized cost	$ 11,997,330	$ 12,419,905
Allowance for expected credit losses	(4,183)	(3,938)	$ (4,237)	$ (10,759)
Gross unrealized gains	80,097	48,121
Gross unrealized losses	(207,764)	(311,335)
Fair value	11,865,480	12,152,753
U.S. government and agency
Available for sale
Amortized cost	2,550,984	2,830,111
Allowance for expected credit losses	0	0
Gross unrealized gains	14,930	6,011
Gross unrealized losses	(12,071)	(33,136)
Fair value	2,553,843	2,802,986
Non-U.S. government
Available for sale
Amortized cost	719,115	753,315
Allowance for expected credit losses	(59)	0
Gross unrealized gains	8,044	2,584
Gross unrealized losses	(12,575)	(25,960)
Fair value	714,525	729,939
Corporate debt
Available for sale
Amortized cost	4,690,383	4,941,510
Allowance for expected credit losses	(3,875)	(3,690)
Gross unrealized gains	38,761	30,594
Gross unrealized losses	(97,659)	(126,224)
Fair value	4,627,610	4,842,190
Agency RMBS
Available for sale
Amortized cost	1,591,388	1,245,681
Allowance for expected credit losses	0	0
Gross unrealized gains	8,903	1,154
Gross unrealized losses	(42,737)	(61,990)
Fair value	1,557,554	1,184,845
CMBS
Available for sale
Amortized cost	879,004	852,534
Allowance for expected credit losses	0	0
Gross unrealized gains	3,347	1,244
Gross unrealized losses	(26,243)	(34,170)
Fair value	856,108	819,608
Non-agency RMBS
Available for sale
Amortized cost	195,220	132,116
Allowance for expected credit losses	(196)	(195)
Gross unrealized gains	731	597
Gross unrealized losses	(6,016)	(9,982)
Fair value	189,739	122,536
ABS
Available for sale
Amortized cost	1,296,928	1,547,350
Allowance for expected credit losses	(53)	(53)
Gross unrealized gains	5,120	5,812
Gross unrealized losses	(8,121)	(13,277)
Fair value	1,293,874	1,539,832
Municipals
Available for sale
Amortized cost	74,308	117,288
Allowance for expected credit losses	0	0
Gross unrealized gains	261	125
Gross unrealized losses	(2,342)	(6,596)
Fair value	$ 72,227	$ 110,817