INVESTMENTS - Contractual Maturities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Amortized cost
Due in one year or less	$ 608,109	$ 422,039
Due after one year through five years	5,408,673	5,349,123
Due after five years through ten years	2,139,206	2,192,344
Due after ten years	172,751	234,046
Total fixed maturities with a single maturity date	8,328,739	8,197,552
Amortized cost, Total	12,272,258	12,176,473
Fair value
Due in one year or less	591,621	409,972
Due after one year through five years	5,166,273	5,078,273
Due after five years through ten years	1,936,227	1,919,450
Due after ten years	160,858	205,575
Total fixed maturities with a single maturity date	7,854,979	7,613,270
Fair value, Total	$ 11,564,397	$ 11,326,894
% of Total fair value
Due in one year or less	5.20%	3.70%
Due after one year through five years (as a percent)	44.70%	44.80%
Due after five years through ten years (as a percent)	16.70%	16.90%
Due after ten years (as a percent)	1.40%	1.80%
Fixed maturities with a single maturity date (as a percent)	68.00%	67.20%
Total (as a percent)	100.00%	100.00%
Agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 1,496,299	$ 1,297,423
Amortized cost, Total	1,496,299	1,297,423
Fair value
Fixed maturities without a single maturity date	1,403,654	1,202,785
Fair value, Total	$ 1,403,654	$ 1,202,785
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	12.10%	10.60%
CMBS
Amortized cost
Fixed maturities without a single maturity date	$ 950,340	$ 1,029,863
Amortized cost, Total	950,340	1,029,863
Fair value
Fixed maturities without a single maturity date	871,107	947,778
Fair value, Total	$ 871,107	$ 947,778
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	7.50%	8.40%
Non-agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 149,827	$ 151,907
Amortized cost, Total	149,827	151,907
Fair value
Fixed maturities without a single maturity date	134,101	133,534
Fair value, Total	$ 134,101	$ 133,534
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	1.20%	1.20%
ABS
Amortized cost
Fixed maturities without a single maturity date	$ 1,347,053	$ 1,499,728
Amortized cost, Total	1,347,053	1,499,728
Fair value
Fixed maturities without a single maturity date	1,300,556	1,429,527
Fair value, Total	$ 1,300,556	$ 1,429,527
% of Total fair value
Fixed maturities without a single maturity date (as a percent)	11.20%	12.60%
Held-to-maturity securities without a single maturity date	$ 627,000	$ 613,000
Corporate debt
Amortized cost
Amortized cost, Total	4,655,745	4,680,798
Fair value
Fair value, Total	4,327,608	4,255,556
% of Total fair value
Held-to-maturity securities with maturity after three years through 10 years	86,000	81,000
Held-to-maturity securities with maturity after ten years	$ 4,000	$ 4,000
Corporate debt | Minimum
% of Total fair value
Debt securities, held-to-maturity, maturity period	3 years
Corporate debt | Maximum
% of Total fair value
Debt securities, held-to-maturity, maturity period	10 years