DERIVATIVE FINANCIAL INSTRUMENTS - Realized Investments Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	$ 46,826	$ (60,900)
Derivatives not designated as hedging instruments
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	46,826	(60,900)
Derivatives not designated as hedging instruments | Embedded derivative - Modco reinsurance treaties
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	82,658	(17,865)
Derivatives not designated as hedging instruments | Derivatives with PLC
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	11,543	(14,875)
Derivatives not designated as hedging instruments | Other derivatives
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(40)	3
Derivatives not designated as hedging instruments | VA
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(62,605)	(26,751)
Derivatives not designated as hedging instruments | VA | Interest rate futures
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(16,892)	3,448
Derivatives not designated as hedging instruments | VA | Equity futures
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(6,428)	(30,817)
Derivatives not designated as hedging instruments | VA | Currency futures
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(7,583)	(6,256)
Derivatives not designated as hedging instruments | VA | Equity options
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	12,016	(40,185)
Derivatives not designated as hedging instruments | VA | Interest rate swaptions
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(14)	(1,469)
Derivatives not designated as hedging instruments | VA | Interest rate swaps
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(63,710)	(8,957)
Derivatives not designated as hedging instruments | VA | Total return swaps
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	6,490	0
Derivatives not designated as hedging instruments | VA | Embedded derivative - GLWB
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	21,473	10,016
Derivatives not designated as hedging instruments | VA | Funds withheld derivative
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(7,957)	47,469
Derivatives not designated as hedging instruments | FIA
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	6,500	(1,414)
Derivatives not designated as hedging instruments | FIA | Equity futures
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(161)	297
Derivatives not designated as hedging instruments | FIA | Equity options
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(4,669)	10,700
Derivatives not designated as hedging instruments | FIA | Embedded derivative - FIA
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	11,330	(12,411)
Derivatives not designated as hedging instruments | IUL
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	8,770	2
Derivatives not designated as hedging instruments | IUL | Equity futures
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	136	(799)
Derivatives not designated as hedging instruments | IUL | Equity options
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	(1,250)	2,891
Derivatives not designated as hedging instruments | IUL | Embedded derivative - IUL
Notional amount and fair value of the entity's derivative financial instruments
Realized investment gains (losses) - derivatives, gross	$ 9,884	$ (2,090)