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FINANCIAL INSTRUMENTS (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of fair value measurement of assets [line items]      
Short-term investments $ 18,252    
Long-term investments 60,630 $ 61,293 $ 26,580
Total assets 660,915 534,882  
Recurring fair value measurement [member]      
Disclosure of fair value measurement of assets [line items]      
Total assets 78,882 61,293  
Recurring fair value measurement [member] | Level 1 of fair value hierarchy [member]      
Disclosure of fair value measurement of assets [line items]      
Total assets 43,974 28,850  
Recurring fair value measurement [member] | Level 2 of fair value hierarchy [member]      
Disclosure of fair value measurement of assets [line items]      
Total assets 34,908 32,443  
Recurring fair value measurement [member] | Covertible Debt [member]      
Disclosure of fair value measurement of assets [line items]      
Short-term investments 15,000    
Long-term investments 16,595 29,039  
Recurring fair value measurement [member] | Covertible Debt [member] | Level 2 of fair value hierarchy [member]      
Disclosure of fair value measurement of assets [line items]      
Short-term investments 15,000    
Long-term investments 16,595 29,039  
Recurring fair value measurement [member] | Warrants [member]      
Disclosure of fair value measurement of assets [line items]      
Long-term investments 3,313 3,404  
Recurring fair value measurement [member] | Warrants [member] | Level 2 of fair value hierarchy [member]      
Disclosure of fair value measurement of assets [line items]      
Long-term investments 3,313 3,404  
Recurring fair value measurement [member] | Common Shares Held [member]      
Disclosure of fair value measurement of assets [line items]      
Short-term investments 3,252    
Long-term investments 40,722 28,850  
Recurring fair value measurement [member] | Common Shares Held [member] | Level 1 of fair value hierarchy [member]      
Disclosure of fair value measurement of assets [line items]      
Short-term investments 3,252    
Long-term investments $ 40,722 $ 28,850