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SHAREHOLDERS' EQUITY AND SHARE-BASED COMPENSATION - Stock option activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Number of options      
Outstanding at the beginning of the period (in shares) 1,745,906    
Granted (in shares) 276,876 244,000 145,000
Exercised (in shares) (330,537)    
Forfeited (in shares) (251,679)    
Outstanding at the end of the period (in shares) 1,440,566 1,745,906  
Exercisable at the end of the period (in shares) 874,304    
Weighted average exercise price      
Outstanding at the beginning of the period (in dollars per share) $ 28.20    
Granted (in dollars per share) 25.15 $ 33.28 $ 29.17
Exercised (in dollars per share) 11.33    
Forfeited (in dollars per share) 32.21    
Outstanding at the end of the period (in dollars per share) 30.78 $ 28.20  
Exercisable at the end of the period (in dollars per share) $ 27.42    
Weighted average contractual term (in years)      
Weighted average contractual term 5 years 14 days 4 years 11 months 16 days  
Exercisable at the end of the period 3 years 2 months 12 days    
Aggregate intrinsic value (in thousands)      
Aggregate intrinsic value (in dollars) $ 945 $ 10,202  
Exercisable at the end of the period (in dollars) $ 902