CERTAIN NONTRADITIONAL LONG-DURATION CONTRACTS - Account Balances and Deferred Sales Inducement Asset (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017
Activity in the Company's deferred sales inducement asset
Deferred asset, beginning of period	$ 11,756	$ 30,956	$ 22,497
Amounts deferred	16,212	13,336	14,246
Amortization	$ (5,471)	(4,715)	(5,787)
Deferred asset, end of period		39,577	30,956
VA
Certain Nontraditional Long-duration Contracts
Account balances of variable annuities with guarantees invested in variable annuity separate accounts		11,868,599	13,734,986
Equity mutual funds \| VA
Certain Nontraditional Long-duration Contracts
Account balances of variable annuities with guarantees invested in variable annuity separate accounts		5,300,024	8,914,637
Fixed income mutual funds \| VA
Certain Nontraditional Long-duration Contracts
Account balances of variable annuities with guarantees invested in variable annuity separate accounts		$ 6,568,575	$ 4,820,349

Amount of addition in deferred sales inducement cost.

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Amount of amortization expense (reversal of expense) for deferred sales inducement cost.

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Amount, after accumulated amortization, of deferred sales inducement cost.

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