Income taxes (Details) - Components of loss before income taxes - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Income taxes (Details) - Components of loss before income taxes [Line Items]
Income (loss) before taxes	$ 37,068	$ (2,113)	$ 7,039	$ 4,521	$ 8,523	$ (3,003)	$ (4,206)	$ (3,606)	$ 46,515	$ (2,292)	$ (9,905)
Domestic Tax Authority [Member]
Income taxes (Details) - Components of loss before income taxes [Line Items]
Income (loss) before taxes									48,847	(615)	(8,702)
Foreign Tax Authority [Member]
Income taxes (Details) - Components of loss before income taxes [Line Items]
Income (loss) before taxes									$ (2,332)	$ (1,677)	$ (1,203)