INVESTMENTS (Contractual Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized cost
Due in one year or less	$ 367,208	$ 438,881
Due after one year through five years	4,318,770	4,810,202
Due after five years through ten years	2,524,796	2,091,486
Due after ten years	257,977	327,444
Total fixed maturities with a single maturity date	7,468,751	7,668,013
Amortized Cost, Total	12,201,832	12,263,240
Fair value
Due in one year or less	371,864	443,228
Due after one year through five years	4,446,778	4,884,837
Due after five years through ten years	2,660,506	2,157,157
Due after ten years	266,544	341,732
Total fixed maturities with a single maturity date	7,745,692	7,826,954
Fair value	$ 12,609,241	$ 12,468,205
% of Total fair value
Due in one year or less	2.80%	3.60%
Due after one year through five years	35.30%	39.20%
Due after five years through ten years	21.10%	17.30%
Due after ten years	2.10%	2.70%
Fixed maturities with a single maturity date	61.30%	62.80%
Total	100.00%	100.00%
Agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 1,630,014	$ 1,570,823
Amortized Cost, Total	1,630,014	1,570,823
Fair value
Fixed maturities without a single maturity date	1,677,106	1,592,584
Fair value	$ 1,677,106	$ 1,592,584
% of Total fair value
Fixed maturities without a single maturity date	13.30%	12.80%
CMBS
Amortized cost
Fixed maturities without a single maturity date	$ 1,291,291	$ 1,340,156
Amortized Cost, Total	1,291,291	1,340,156
Fair value
Fixed maturities without a single maturity date	1,380,738	1,365,052
Fair value	$ 1,380,738	$ 1,365,052
% of Total fair value
Fixed maturities without a single maturity date	11.00%	10.90%
Non-agency RMBS
Amortized cost
Fixed maturities without a single maturity date	$ 131,937	$ 84,381
Amortized Cost, Total	131,937	84,381
Fair value
Fixed maturities without a single maturity date	133,530	84,922
Fair value	$ 133,530	$ 84,922
% of Total fair value
Fixed maturities without a single maturity date	1.10%	0.70%
ABS
Amortized cost
Fixed maturities without a single maturity date	$ 1,679,839	$ 1,599,867
Amortized Cost, Total	1,679,839	1,599,867
Fair value
Fixed maturities without a single maturity date	1,672,175	1,598,693
Fair value	$ 1,672,175	$ 1,598,693
% of Total fair value
Fixed maturities without a single maturity date	13.30%	12.80%