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Equity (Details) - USD ($)
$ in Thousands, shares in Millions
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Oct. 27, 2016
Purchase of treasury stock $ 42,321 $ 64,101  
Treasury Stock [Member]      
Purchase of treasury stock $ 42,321 $ 64,101  
Class B [Member]      
Number of shares authorized under share repurchase program     4.0
Repurchased shares 1.6    
Remaining number of shares authorized to be repurchased 2.3