INVESTMENT OPERATIONS - Schedule of Available-for-Sale Credit Losses on Fixed Maturities Held by the Company for Which a Portion of Other-than-Temporary Impairments were Recognized in Other Comprehensive Income (Loss) (Details) - Fixed maturities - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 2	$ 2,783	$ 3,268	$ 12,685
Additions for newly impaired securities	0	266	0	266
Additions for previously impaired securities	0	6	2	2,791
Reductions for previously impaired securities due to a change in expected cash flows	0	(37)	0	(12,724)
Reductions for previously impaired securities that were sold in the current period	(2)	(600)	(3,270)	(600)
Ending balance	$ 0	$ 2,418	$ 0	$ 2,418