INVESTMENT OPERATIONS - Schedule of Gross Realized Gains and Losses on Available-for-Sale Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 61,608	$ 28,034	$ 18,868
Gross realized losses:
Impairments losses	(34,453)	(29,724)	(9,112)
Other realized losses	$ (13,897)	$ (18,183)	$ (8,257)