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STOCKHOLDERS' EQUITY, Repurchase of Common Stock (Details) - $ / shares
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Repurchase of common stock [Abstract]      
Number of shares authorized to be repurchased (in shares) 3,763,038    
Aggregate number of shares repurchased since inception (in shares) 2,188,879    
Number of shares remaining in treasury (in shares) 4,408   0
Number of shares acquired under stock repurchase plan and subsequently reissued (in shares) 14,862 21,099  
Treasury stock acquired, average cost (in dollars per share) $ 82.22 $ 82.53