INVESTMENTS (Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Amortized cost
Due in one year or less	$ 524,297	$ 436,287
Due after one year through five years	4,651,630	4,165,696
Due after five years through ten years	2,435,663	2,344,859
Due after ten years	209,067	258,654
Total fixed maturities with a single maturity date	7,820,657	7,205,496
Amortized Cost, Total	11,638,359	11,566,930
Fair value
Due in one year or less	531,246	444,527
Due after one year through five years	4,761,285	4,335,219
Due after five years through ten years	2,495,245	2,489,050
Due after ten years	214,248	273,025
Total fixed maturities with a single maturity date	8,002,024	7,541,821
Fair value	$ 11,898,300	$ 12,041,799
% of Total fair value
Due in one year or less	4.50%	3.60%
Due after one year through five years	40.00%	36.00%
Due after five years through ten years	21.00%	20.70%
Due after ten years	1.80%	2.30%
Fixed maturities with a single maturity date	67.30%	62.60%
Total	100.00%	100.00%
Agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 1,022,259	$ 1,244,727
Amortized Cost, Total	1,022,259	1,244,727
Fair value
Fixed maturities without a single maturity date	1,044,556	1,286,209
Fair value	$ 1,044,556	$ 1,286,209
% of Total fair value
Fixed maturities without a single maturity date	8.80%	10.70%
CMBS
Amortized cost
Fixed maturities without a single maturity date	$ 1,097,457	$ 1,268,273
Amortized Cost, Total	1,097,457	1,268,273
Fair value
Fixed maturities without a single maturity date	1,144,592	1,353,587
Fair value	$ 1,144,592	$ 1,353,587
% of Total fair value
Fixed maturities without a single maturity date	9.60%	11.20%
Non-agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 204,437	$ 136,198
Amortized Cost, Total	204,437	136,198
Fair value
Fixed maturities without a single maturity date	207,489	140,104
Fair value	$ 207,489	$ 140,104
% of Total fair value
Fixed maturities without a single maturity date	1.70%	1.20%
ABS
Amortized cost
Fixed maturities without a single maturity date	$ 1,493,549	$ 1,712,236
Amortized Cost, Total	1,493,549	1,712,236
Fair value
Fixed maturities without a single maturity date	1,499,639	1,720,078
Fair value	$ 1,499,639	$ 1,720,078
% of Total fair value
Fixed maturities without a single maturity date	12.60%	14.30%