Income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Income taxes (Details) [Line Items]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 14,700	$ 200
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	55,000
Deferred Tax Assets Research and Development and Other Tax Credit Carryforwards	2,152	$ 1,134
Foreign Loss Carryforwards	7,900
Undistributed Earnings of Foreign Subsidiaries	101
Liability for Uncertain Tax Position	0
U.S. Federal Tax [Member]
Income taxes (Details) [Line Items]
Deferred Tax Assets Research and Development and Other Tax Credit Carryforwards	$ 1,000
Minimum [Member] | Domestic Tax Authority [Member]
Income taxes (Details) [Line Items]
Operating Loss Carryforwards Expiration Year	2030
Minimum [Member] | Research Tax Credit Carryforward [Member]
Income taxes (Details) [Line Items]
Tax Credit Carryforward Expiration Year	2025
Maximum [Member] | Domestic Tax Authority [Member]
Income taxes (Details) [Line Items]
Operating Loss Carryforwards Expiration Year	2035
Maximum [Member] | Research Tax Credit Carryforward [Member]
Income taxes (Details) [Line Items]
Tax Credit Carryforward Expiration Year	2036