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SHAREHOLDERS' EQUITY - Accelerated share repurchase program (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 5 Months Ended 12 Months Ended
Jan. 15, 2016
Aug. 20, 2015
Aug. 31, 2015
Jan. 15, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Treasury Stock              
Class of Stock [Line Items]              
Total cost         $ 285,858 $ 571,805 $ 264,538
Additional paid-in capital              
Class of Stock [Line Items]              
Total cost         $ 0 $ (60,000) $ 60,000
Accelerated Share Repurchase Agreement August 17 2015              
Class of Stock [Line Items]              
Total cost     $ 300,000        
Total shares (in shares) 1,358,380 4,149,378 4,149,378 5,507,758   1,358,380 4,149,378
Accelerated Share Repurchases, initial repurchase percentage     80.00%        
Average price per share (in usd per share)       $ 54.47      
Accelerated Share Repurchase Agreement August 17 2015 | Treasury Stock              
Class of Stock [Line Items]              
Total cost $ 60,000           $ 240,000
Accelerated Share Repurchase Agreement August 17 2015 | Additional paid-in capital              
Class of Stock [Line Items]              
Total cost             $ 60,000