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INVESTMENTS - Fixed Maturities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Available for sale
Amortized cost	$ 13,009,189		$ 12,634,254
Allowance for expected credit losses	(4,631)	$ (4,237)	(10,759)	$ (10,551)	$ (12,645)	$ (11,733)
Gross unrealized gains	46,364		91,762
Gross unrealized losses	(465,785)		(480,515)
Fair value	12,585,137		12,234,742
U.S. government and agency
Available for sale
Amortized cost	2,713,759		3,049,445
Allowance for expected credit losses	0		0
Gross unrealized gains	6,506		13,211
Gross unrealized losses	(47,299)		(55,128)
Fair value	2,672,966		3,007,528
Non-U.S. government
Available for sale
Amortized cost	771,227		729,761
Allowance for expected credit losses	(74)		(30)
Gross unrealized gains	3,605		13,089
Gross unrealized losses	(23,250)		(18,861)
Fair value	751,508		723,959
Corporate debt
Available for sale
Amortized cost	5,271,600		4,651,654
Allowance for expected credit losses	(4,303)		(10,438)
Gross unrealized gains	30,067		49,434
Gross unrealized losses	(210,837)		(216,478)
Fair value	5,086,527		4,474,172
Agency RMBS
Available for sale
Amortized cost	1,692,741		1,706,204
Allowance for expected credit losses	0		0
Gross unrealized gains	2,304		11,495
Gross unrealized losses	(94,018)		(83,038)
Fair value	1,601,027		1,634,661
CMBS
Available for sale
Amortized cost	874,187		897,553
Allowance for expected credit losses	0		0
Gross unrealized gains	540		551
Gross unrealized losses	(50,012)		(58,408)
Fair value	824,715		839,696
Non-agency RMBS
Available for sale
Amortized cost	138,135		165,910
Allowance for expected credit losses	(203)		(194)
Gross unrealized gains	456		713
Gross unrealized losses	(11,624)		(13,033)
Fair value	126,764		153,396
ABS
Available for sale
Amortized cost	1,386,533		1,265,187
Allowance for expected credit losses	(51)		(50)
Gross unrealized gains	2,661		2,855
Gross unrealized losses	(18,499)		(25,021)
Fair value	1,370,644		1,242,971
Municipals
Available for sale
Amortized cost	161,007		168,540
Allowance for expected credit losses	0		(47)
Gross unrealized gains	225		414
Gross unrealized losses	(10,246)		(10,548)
Fair value	$ 150,986		$ 158,359