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	793,423
Due after one year through five years	6,068,649
Due after five years through ten years	7,503,015
Due after ten years	22,691,135
Total	37,056,222
Available-for-sale, Fair Value
Due in one year or less	793,702
Due after one year through five years	6,084,212
Due after five years through ten years	7,504,505
Due after ten years	22,099,507
Total	36,481,926
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