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 (Details) - Fixed maturities - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Credit losses on fixed maturities
Beginning balance	$ 3,268	$ 12,685	$ 22,761
Additions for newly impaired securities	24,858	734	14,876
Additions for previously impaired securities	12	3,175	2,063
Reductions for previously impaired securities due to a change in expected cash flows	0	(12,726)	(24,396)
Reductions for previously impaired securities that were sold in the current period	(3,270)	(600)	(2,619)
Other	0	0	0
Ending balance	$ 24,868	$ 3,268	$ 12,685