INVESTMENT OPERATIONS - Summary of Change in Unrealized Gains (Losses), Net of Income Tax, on Fixed Maturity and Equity Securities Classified as Available-for-Sale (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fixed maturities
Investment [Line Items]
Change in unrealized gains (losses) net of income tax	$ (2,041,445)	$ 1,086,727	$ 802,368

Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration