INVESTMENTS - Gross Unrealized Losses (Details) $ in Thousands	Jun. 30, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Fair value
12 months or greater	$ 4,967,984	$ 6,293,107
Less than 12 months	3,566,492	1,617,343
Total	8,534,476	7,910,450
Unrealized losses
12 months or greater	(423,271)	(453,997)
Less than 12 months	(42,514)	(26,518)
Total	$ (465,785)	$ (480,515)
Number of securities in unrealized loss position | security	4,248	3,535
Number of securities in a continuous unrealized loss position | security	2,909	3,212
Below Investment Grade or Not Rated
Unrealized losses
Total	$ (12,000)	$ (13,000)
U.S. government and agency
Fair value
12 months or greater	613,647	846,503
Less than 12 months	1,129,410	867,733
Total	1,743,057	1,714,236
Unrealized losses
12 months or greater	(36,799)	(42,465)
Less than 12 months	(10,500)	(12,663)
Total	(47,299)	(55,128)
Non-U.S. government
Fair value
12 months or greater	211,122	233,038
Less than 12 months	348,236	115,112
Total	559,358	348,150
Unrealized losses
12 months or greater	(18,833)	(18,178)
Less than 12 months	(4,417)	(683)
Total	(23,250)	(18,861)
Corporate debt
Fair value
12 months or greater	2,173,470	2,623,304
Less than 12 months	1,202,422	240,813
Total	3,375,892	2,864,117
Unrealized losses
12 months or greater	(194,191)	(210,512)
Less than 12 months	(16,646)	(5,966)
Total	(210,837)	(216,478)
Agency RMBS
Fair value
12 months or greater	765,043	778,656
Less than 12 months	501,789	218,606
Total	1,266,832	997,262
Unrealized losses
12 months or greater	(87,306)	(80,070)
Less than 12 months	(6,712)	(2,968)
Total	(94,018)	(83,038)
CMBS
Fair value
12 months or greater	666,929	703,411
Less than 12 months	81,346	75,242
Total	748,275	778,653
Unrealized losses
12 months or greater	(47,722)	(54,856)
Less than 12 months	(2,290)	(3,552)
Total	(50,012)	(58,408)
Non-agency RMBS
Fair value
12 months or greater	77,872	98,483
Less than 12 months	10,373	10,017
Total	88,245	108,500
Unrealized losses
12 months or greater	(11,582)	(13,013)
Less than 12 months	(42)	(20)
Total	(11,624)	(13,033)
ABS
Fair value
12 months or greater	342,311	879,743
Less than 12 months	272,328	83,582
Total	614,639	963,325
Unrealized losses
12 months or greater	(17,096)	(24,747)
Less than 12 months	(1,403)	(274)
Total	(18,499)	(25,021)
Municipals
Fair value
12 months or greater	117,590	129,969
Less than 12 months	20,588	6,238
Total	138,178	136,207
Unrealized losses
12 months or greater	(9,742)	(10,156)
Less than 12 months	(504)	(392)
Total	$ (10,246)	$ (10,548)