SUMMARY OF INVESTMENTS (Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Held-To-Maturity, Amortized Cost
Held-to-maturity securities, amortized cost	$ 198	$ 672
Held-To-Maturity, Fair Value
Held-to-maturity securities	199	675
Amortized Cost
Available-for-sale securities, amortized cost	2,956,009	2,861,583
Fair Value
Available-for-sale securities	3,168,542	3,061,208
Fair Value
Trading securities, fair value	14,390	12,622
Asset-backed securities
Amortized Cost
Available-for-sale securities, amortized cost	4,407	5,461
Fair Value
Available-for-sale securities	4,270	5,666
Mortgage-backed securities
Held-To-Maturity, Amortized Cost
Held-to-maturity securities, amortized cost	48	72
Held-To-Maturity, Fair Value
Held-to-maturity securities	49	74
Amortized Cost
Available-for-sale securities, amortized cost	17,288	16,413
Fair Value
Available-for-sale securities	17,248	$ 16,738
Fixed Maturities
Held-To-Maturity, Amortized Cost
Due in one year or less	150
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	0
Held-to-maturity securities, amortized cost	198
Held-To-Maturity, Fair Value
Due in one year or less	150
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	0
Held-to-maturity securities	199
Amortized Cost
Due in one year or less	106,058
Due after one year through five years	840,603
Due after five years through 10 years	807,723
Due after 10 years	687,839
Available-for-sale securities, amortized cost	2,887,505
Fair Value
Due in one year or less	107,080
Due after one year through five years	862,053
Due after five years through 10 years	815,182
Due after 10 years	671,479
Available-for-sale securities	2,898,126
Amortized Cost
Due in one year or less	1,753
Due after one year through five years	7,841
Due after five years through 10 years	1,302
Due after 10 years	2,158
Trading securities, amortized cost	13,054
Fair Value
Due in one year or less	1,774
Due after one year through five years	8,882
Due after five years through 10 years	1,406
Due after 10 years	2,328
Trading securities, fair value	14,390
Fixed Maturities | Asset-backed securities
Held-To-Maturity, Amortized Cost
Not categorized by contractual maturity	0
Held-To-Maturity, Fair Value
Not categorized by contractual maturity	0
Amortized Cost
Not categorized by contractual maturity	4,407
Fair Value
Not categorized by contractual maturity	4,270
Fixed Maturities | Mortgage-backed securities
Held-To-Maturity, Amortized Cost
Not categorized by contractual maturity	48
Held-To-Maturity, Fair Value
Not categorized by contractual maturity	49
Amortized Cost
Not categorized by contractual maturity	17,288
Fair Value
Not categorized by contractual maturity	17,248
Fixed Maturities | Collateralized mortgage obligations
Held-To-Maturity, Amortized Cost
Not categorized by contractual maturity	0
Held-To-Maturity, Fair Value
Not categorized by contractual maturity	0
Amortized Cost
Not categorized by contractual maturity	423,587
Fair Value
Not categorized by contractual maturity	$ 420,814