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FINANCIAL INSTRUMENTS - Fair value measurements for financial instruments (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Aug. 03, 2016
5% Convertible Debentures      
Disclosure of financial liabilities [line items]      
Borrowings, interest rate 5.00% 5.00%  
7% Convertible Debentures      
Disclosure of financial liabilities [line items]      
Borrowings, interest rate 7.00%   7.00%
Carrying value | Level 3 | Convertible Debentures | 7% Convertible Debentures      
Disclosure of financial liabilities [line items]      
Financial Liabilities $ 4,177 $ 10,963  
Fair value | Level 3 | Convertible Debentures | 7% Convertible Debentures      
Disclosure of financial liabilities [line items]      
Financial Liabilities $ 4,177 $ 10,963