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Marketable Securities (Details Textual) - USD ($)
$ in Millions
12 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Jul. 31, 2013
Marketable Securities [Abstract]      
Company received number of Straight Path Class B common stock, shares 64,624    
Proceeds from maturities of available-for-sale securities $ 24.1 $ 17.3 $ 1.7
Realized losses from sales of available-for-sale securities 0.1  
Realized gains from sales of available-for-sale securities $ 0.0 $ 0.0 $ 0.0
Unrealized losses, less than twelve months or longer  
Other than temporary impairment losses, investments, available-for-sale securities   $ 0.1