INVESTMENT OPERATIONS - Summary of Net Realized Investment Gains (Losses) for all Other Investments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Fixed maturities	$ 1,098	$ 5,539	$ 6,215	$ 8,322
Equity gains and losses	7,696	(1,044)	38,413	(9,830)
Modco trading portfolio	89,571	(52,817)	184,473	(137,525)
Other investments	1,137	(1,280)	(9)	1,832
Realized gains (losses) - all other investments	99,502	(49,602)	229,092	(137,201)
Derivative financial instruments	(148,049)	12,265	(267,720)	90,324
Realized investment gains (losses)	(48,547)	(37,337)	(38,628)	(46,877)
Net impairments losses recognized in earnings	$ (698)	$ (5)	$ (3,840)	$ (3,650)

Realized Investment Gains (Losses), All Investments

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Represents the total realized gain (loss) included in earnings during the period as a result of investments other than derivative financial instruments, net of the amount recognized in earnings for other than temporary impairments (OTTI) of investments in debt and equity securities.

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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Amount of gain (loss) included in earnings for investments classified as other.

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Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

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