INVESTMENT OPERATIONS - Schedule of Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Fixed Maturities, by Expected Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Held-to-maturity, Fair Value
Fair Value	$ 2,805,107	$ 2,733,340
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	797,232
Due after one year through five years	6,083,410
Due after five years through ten years	7,646,402
Due after ten years	22,726,160
Amortized Cost	37,253,204
Available-for-sale, Fair Value
Due in one year or less	797,523
Due after one year through five years	6,099,182
Due after five years through ten years	7,649,742
Due after ten years	22,135,377
Fair Value	36,681,824
Held-to-maturity, Amortized Cost
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	2,747,077
Amortized Cost	2,747,077	2,770,177
Held-to-maturity, Fair Value
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	2,805,107
Fair Value	$ 2,805,107	$ 2,733,340