DERIVATIVE FINANCIAL INSTRUMENTS - Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	$ (108,188)	$ (83,366)	$ (178,066)	$ (156,865)
Derivatives not designated as hedging instruments
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(108,188)	(83,366)	(178,066)	(156,865)
Derivatives not designated as hedging instruments | Embedded derivative - Modco reinsurance treaties
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(52,703)	(22,820)	(70,568)	(81,175)
Derivatives not designated as hedging instruments | Other derivatives
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(5)	(55)	(2)	(100)
Derivatives not designated as hedging instruments | VA
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(46,376)	(62,779)	(96,980)	(70,552)
Derivatives not designated as hedging instruments | VA | Interest rate futures
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	12,749	31,266	16,197	69,067
Derivatives not designated as hedging instruments | VA | Equity futures
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(18,613)	(21,328)	(49,430)	(24,556)
Derivatives not designated as hedging instruments | VA | Currency futures
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(10,018)	11,112	(16,274)	4,954
Derivatives not designated as hedging instruments | VA | Equity options
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(12,884)	(3,232)	(53,069)	13,072
Derivatives not designated as hedging instruments | VA | Interest rate swaptions
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(662)	(749)	(2,131)	(2,983)
Derivatives not designated as hedging instruments | VA | Interest rate swaps
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	34,946	81,554	25,989	207,147
Derivatives not designated as hedging instruments | VA | Total return swaps
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(1,618)	0	(1,618)	0
Derivatives not designated as hedging instruments | VA | Embedded derivative - GLWB
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(50,276)	(161,402)	(16,644)	(337,253)
Derivatives not designated as hedging instruments | FIA
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(1,967)	2,096	(3,381)	(4,246)
Derivatives not designated as hedging instruments | FIA | Equity futures
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(202)	651	95	2,033
Derivatives not designated as hedging instruments | FIA | Equity options
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	7,569	735	18,269	(4,827)
Derivatives not designated as hedging instruments | FIA | Embedded derivative - FIA
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(9,334)	710	(21,745)	(1,452)
Derivatives not designated as hedging instruments | FIA | Volatility futures
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	0	0	0	0
Derivatives not designated as hedging instruments | IUL
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(7,137)	192	(7,135)	(792)
Derivatives not designated as hedging instruments | IUL | Equity futures
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(137)	47	(936)	(172)
Derivatives not designated as hedging instruments | IUL | Equity options
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	1,571	241	4,462	214
Derivatives not designated as hedging instruments | IUL | Embedded derivative - IUL
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	$ (8,571)	$ (96)	$ (10,661)	$ (834)