DERIVATIVES AND HEDGING - Summary of Freestanding Derivative Instruments on Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gains and losses from freestanding derivative instruments	$ (7,252)	$ (6,086)	$ (25,531)	$ (26,569)
Investment income | Not Designated as Hedging Instrument | Foreign-currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains and losses from freestanding derivative instruments	(4,141)	(802)	(13,469)	(3,173)
General and administrative expense | Not Designated as Hedging Instrument | Foreign-currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains and losses from freestanding derivative instruments	$ (3,111)	$ (5,284)	$ (12,062)	$ (23,396)