FINANCIAL INSTRUMENTS - Activity for Financial Instrument Liabilities and Related Restricted Cash (Details) - Not designated as hedging instrument - Foreign instruments and restricted cash - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Foreign Currency Financial Liabilities and Related Restricted Cash [Roll Forward]
Balance, beginning of period	$ 15,629	$ 12,640
Short sales of corporate securities	26	165
Net investment (gains) losses	(121)	2,918
Balance, end of period	12,434	15,629
Equity contracts
Foreign Currency Financial Liabilities and Related Restricted Cash [Roll Forward]
Settlement of short sales of corporate securities	$ (3,100)	$ (94)