INVESTMENT OPERATIONS - Summary of Other-than-Temporary Impairments of Investments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Other-than-temporary impairments									$ (56,578)	$ (1,332)	$ (32,075)
Non-credit impairment losses recorded in other comprehensive income									26,854	(7,780)	14,327
Net impairment losses recognized in earnings	$ (26,060)	$ (14)	$ (5)	$ (3,645)	$ (853)	$ (273)	$ (2,785)	$ (5,201)	(29,724)	(9,112)	(17,748)
Fixed Maturities
Investment Holdings [Line Items]
Other-than-temporary impairments									(56,578)	(1,332)	(32,075)
Non-credit impairment losses recorded in other comprehensive income									26,854	(7,780)	14,327
Net impairment losses recognized in earnings									(29,724)	(9,112)	(17,748)
Equity securities
Investment Holdings [Line Items]
Other-than-temporary impairments									0	0	0
Non-credit impairment losses recorded in other comprehensive income									0	0	0
Net impairment losses recognized in earnings									$ 0	$ 0	$ 0