Goodwill and intangible assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Goodwill and intangible assets (Details) [Line Items]
Goodwill	$ 7,452	$ 7,452
Finite-Lived Intangible Asset, Useful Life	10 years
Amortization of Intangible Assets	$ 1,677	$ 1,770	$ 1,840
Intangible Assets, Amortization Period [Member]
Goodwill and intangible assets (Details) [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years