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SHARE-BASED AWARDS AND OPTIONS - Stock Options Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 14,833 $ 9,617 $ 44,937 $ 30,771
Employee stock option        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense 700 $ 700 2,300 2,000
Aggregate intrinsic value of stock options exercised     15,900 $ 9,900
Total unrecognized compensation cost $ 4,400   $ 4,400  
Weighted-average period of unrecognized compensation cost     2 years  
Weighted average grant date fair value for each option granted (USD per share) $ 35.09 $ 23.68 $ 35.09 $ 23.68