Marketable Securities (Details Textual) - USD ($)	2 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2015	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2016	Apr. 30, 2015	Jul. 31, 2015
Marketable Securities (Textual)
Company received number of Straight Path Class B common stock, Value				$ 24,176,000	$ 16,840,000
Realized gains (losses) from sales of available-for-sale securities				500,000	(54,000)
Proceeds from maturities of available-for-sale securities		$ 5,500,000	$ 4,700,000	$ 24,200,000	$ 16,800,000
Realized gains (losses) from sales excluding temporary impairment
Straight Path Class B shares [Member]
Marketable Securities (Textual)
Company received number of Straight Path Class B common stock, shares						64,624
Company received number of Straight Path Class B common stock, Value	$ 2,600,000
Realized gains (losses) from sales of available-for-sale securities	$ 500,000
Payment of an aggregate for employee tax withholding on Straight Path shares						$ 2,100,000