INVESTMENTS - Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Amortized cost
Due in one year or less	$ 799,006	$ 895,177
Due after one year through five years	5,222,543	5,637,336
Due after five years through ten years	1,835,434	1,895,116
Due after ten years	177,807	214,595
Total fixed maturities with a single maturity date	8,034,790	8,642,224
Amortized cost, total	11,997,330	12,419,905
Fair value
Due in one year or less	793,243	885,866
Due after one year through five years	5,199,338	5,567,905
Due after five years through ten years	1,803,925	1,826,564
Due after ten years	171,699	205,597
Total fixed maturities with a single maturity date	7,968,205	8,485,932
Fair value, total	$ 11,865,480	$ 12,152,753
% of Total fair value
Due in one year or less (as a percent)	6.80%	7.40%
Due after one year through five years (as a percent)	43.80%	45.80%
Due after five years through ten years (as a percent)	15.20%	15.00%
Due after ten years (as a percent)	1.40%	1.70%
Fixed maturities with a single maturity date (as a percent)	67.20%	69.90%
Total (as a percent)	100.00%	100.00%
Agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 1,591,388	$ 1,245,681
Amortized cost, total	1,591,388	1,245,681
Fair value
Fixed maturities without a single maturity date	1,557,554	1,184,845
Fair value, total	$ 1,557,554	$ 1,184,845
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	13.10%	9.70%
CMBS
Amortized cost
Fixed maturities without a single maturity date	$ 879,004	$ 852,534
Amortized cost, total	879,004	852,534
Fair value
Fixed maturities without a single maturity date	856,108	819,608
Fair value, total	$ 856,108	$ 819,608
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	7.20%	6.70%
Non-agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 195,220	$ 132,116
Amortized cost, total	195,220	132,116
Fair value
Fixed maturities without a single maturity date	189,739	122,536
Fair value, total	$ 189,739	$ 122,536
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	1.60%	1.00%
ABS
Amortized cost
Fixed maturities without a single maturity date	$ 1,296,928	$ 1,547,350
Amortized cost, total	1,296,928	1,547,350
Fair value
Fixed maturities without a single maturity date	1,293,874	1,539,832
Fair value, total	$ 1,293,874	$ 1,539,832
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	10.90%	12.70%