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Equity (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 6 Months Ended
Dec. 14, 2016
Mar. 31, 2017
Jan. 31, 2017
Jan. 31, 2016
Class of Stock [Line Items]        
Dividends paid     $ 8,800 $ 8,600
Dividends paid per share in cash     $ 0.38  
Proceeds from exercise of stock options     $ 835
Class A common stock [Member]        
Class of Stock [Line Items]        
Dividends paid per share in cash     $ 0.38 $ 0.37
Class A common stock [Member] | Subsequent Event [Member]        
Class of Stock [Line Items]        
Common stock dividends declared   $ 0.19    
Paid date of declared dividend   Mar. 24, 2017    
Record date of declared dividend   Mar. 17, 2017    
Class B common stock [Member]        
Class of Stock [Line Items]        
Dividends paid per share in cash     $ 0.38 $ 0.37
Restricted Class B common stock purchased from employees, shares     8,000,000  
Stock repurchase program, remaining number of shares authorized to be repurchased     8,000,000  
Aggregate purchase price of shares repurchased       $ 4,600
Class B common stock shares repurchased       398,376
Number of additional shares authorized 100,000      
Stock issued for stock option exercises     73,471  
Class B common stock [Member] | Employee [Member]        
Class of Stock [Line Items]        
Aggregate purchase price of shares repurchased     $ 1,800 $ 1,000
Class B common stock shares repurchased     94,338 11,250
Class B common stock [Member] | Subsequent Event [Member]        
Class of Stock [Line Items]        
Common stock dividends declared   $ 0.19    
Paid date of declared dividend   Mar. 24, 2017    
Record date of declared dividend   Mar. 17, 2017