DERIVATIVE FINANCIAL INSTRUMENTS - Realized Investments Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	$ (73,308)	$ 46,826
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	(84,998)	82,658
Derivatives not designated as hedging instruments | Derivatives with PLC
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(1,653)	11,543
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	66	(40)
Derivatives not designated as hedging instruments | VA
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	17,489	(62,605)
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	(6,022)	(16,892)
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	29,738	(6,428)
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	2,244	(7,583)
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	(71,695)	12,016
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	0	(14)
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	74,861	(63,710)
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	(40,027)	6,490
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	(33,387)	21,473
Derivatives not designated as hedging instruments | VA | Funds withheld derivative
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	61,777	(7,957)
Derivatives not designated as hedging instruments | FIA
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	2,807	6,500
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	(429)	(161)
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	42,050	(4,669)
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	(38,814)	11,330
Derivatives not designated as hedging instruments | IUL
Notional amount and fair value of the entity's derivative financial instruments
Total realized gains (losses) - derivatives	(7,019)	8,770
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	171	136
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	6,180	(1,250)
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	$ (13,370)	$ 9,884