INVESTMENT OPERATIONS - Schedule of Gross Realized Gains (Losses) on Investments Available-for-Sale (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]
Gross realized gains	$ 20,155	$ 3,410	$ 34,837	$ 21,596
Gross realized losses:
Impairment losses	(10,818)	(14)	(14,658)	(3,664)
Other realized losses	$ (4,469)	$ (5,428)	$ (12,936)	$ (15,292)