INVESTMENT OPERATIONS - Summary of Net Realized Investment Gains (Losses) for all Other Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Fixed maturities	$ 5,539	$ (50)	$ 8,322	$ 9,440
Equity gains and losses	(1,044)	(1,037)	(9,830)	(1,046)
Impairments	(5)	(2,785)	(3,650)	(10,616)
Modco trading portfolio	(52,817)	55,230	(137,525)	73,782
Other investments	(1,280)	(426)	1,832	(5,618)
Total realized gains (losses) - investments	$ (49,607)	$ 50,932	$ (140,851)	$ 65,942