INVESTMENT OPERATIONS - Summary of Net Realized Investment Gains (Losses) for All Other Investments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Fixed maturities	$ 15,686	$ (2,018)	$ 21,885	$ 6,248
Equity gains and losses	6,117	(6,925)	44,292	(16,693)
Modco trading portfolio	67,674	(10,901)	252,147	(148,427)
Other investments	(1,260)	(312)	(1,070)	1,522
Realized gains (losses) - all other investments	88,217	(20,156)	317,254	(157,350)
Realized gains (losses) - derivatives	42,286	(26,710)	(86,288)	37,176
Realized investment gains (losses)	130,503	(46,866)	230,966	(120,174)
Net impairments losses recognized in earnings	$ (10,818)	$ (14)	$ (14,658)	$ (3,664)

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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