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SHARE-BASED AWARDS AND OPTIONS - Stock Options Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense $ 14,898 $ 8,816
Employee stock option    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense 700 600
Aggregate intrinsic value of stock options exercised 2,100 $ 2,800
Total unrecognized compensation cost $ 6,300  
Weighted-average period of unrecognized compensation cost 2 years 150 days  
Weighted average grant date fair value for each option granted (USD per share) $ 35.09 $ 23.68