Income taxes (Details) - Components of loss before income taxes (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2012
Income taxes (Details) - Components of loss before income taxes [Line Items]
Loss before taxes	$ (3,162)	$ (448)	$ (3,570)	$ (2,725)	$ (3,532)	$ (5,808)	$ (5,854)	$ (3,755)	$ (9,905)	$ (18,949)	$ (40,921)
Domestic Tax Authority [Member]
Income taxes (Details) - Components of loss before income taxes [Line Items]
Loss before taxes									(8,702)	(15,419)	(31,817)
Foreign Tax Authority [Member]
Income taxes (Details) - Components of loss before income taxes [Line Items]
Loss before taxes									$ (1,203)	$ (3,530)	$ (9,104)