Summary of Significant Accounting Policies - Revenue (Details) $ in Thousands	12 Months Ended
	Jul. 31, 2018 USD ($) customer	Jul. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)
Revenue recognition - reductions
Number of customers with products shipped FOB destination | customer	1
Volume rebates | $	$ 8,401	$ 6,291	$ 5,944