Summary of significant accounting policies (Details) - Computation of basic and diluted net loss per share - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Computation of basic and diluted net loss per share [Abstract]
Net income (loss) (in Dollars)	$ (5,390)	$ 22,265	$ (8,408)	$ (5,978)	$ (5,758)	$ (3,016)	$ (901)	$ (640)	$ 2,489	$ (10,321)	$ (2,504)
Weighted-average common shares outstanding - basic									47,351	46,972	46,350
Add: effect of dilutive stock options and restricted stock									125
Weighted-average common shares outstanding - diluted									47,476	46,972	46,350
Net (loss) income per share – basic (in Dollars per share)									$ 0.05	$ (0.22)	$ (0.05)
Net (loss) income per share – diluted (in Dollars per share)									$ 0.05	$ (0.22)	$ (0.05)