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	Mar. 31, 2017	Dec. 31, 2016
Held-to-maturity, Fair Value
Fair Value	$ 2,746,375	$ 2,733,340
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	583,614
Due after one year through five years	6,534,001
Due after five years through ten years	7,847,205
Due after ten years	22,271,285
Total	37,236,105
Available-for-sale, Fair Value
Due in one year or less	584,526
Due after one year through five years	6,533,496
Due after five years through ten years	7,767,967
Due after ten years	21,045,522
Total	35,931,511
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	2,758,137
Amortized Cost	2,758,137	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	2,746,375
Fair Value	$ 2,746,375	$ 2,733,340