INVESTMENT OPERATIONS - Schedule of Other-than-Temporary Impairments of Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investment [Line Items]
Other-than-temporary impairment losses	$ (14)	$ (366)	$ (715)	$ (3,124)
Non-credit impairment losses recorded in other comprehensive income	0	93	(2,949)	(7,765)
Net impairment losses recognized in earnings	(14)	(273)	(3,664)	(10,889)
Fixed maturities
Investment [Line Items]
Other-than-temporary impairment losses	(14)	(366)	(715)	(494)
Non-credit impairment losses recorded in other comprehensive income	0	93	(2,949)	(7,765)
Net impairment losses recognized in earnings	$ (14)	(273)	$ (3,664)	(8,259)
Equity securities
Investment [Line Items]
Other-than-temporary impairment losses		0		(2,630)
Non-credit impairment losses recorded in other comprehensive income		0		0
Net impairment losses recognized in earnings		$ 0		$ (2,630)