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Investments - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jan. 31, 2017
Jan. 31, 2018
Jan. 31, 2017
Jul. 31, 2017
Investment [Line Items]        
Sale (purchase) of Trading Securities $ 4,900 $ 13,800 $ 5,800  
Gains (losses) on Trading Securities 1,011 1,876 94  
Trading securities   0   $ 11,898
Cash        
Investment [Line Items]        
Gains (losses) on Trading Securities 600 4,600 600  
Non Cash        
Investment [Line Items]        
Gains (losses) on Trading Securities $ 400 $ (2,700) $ (500)