Segment reporting (Details) - Geographic financial information - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales to unaffiliated customers	$ 102,773	$ 97,599	$ 95,947
Long-lived assets at July 31,
Long-lived assets	20,088	21,555
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales to unaffiliated customers	94,016	87,875	84,389
Long-lived assets at July 31,
Long-lived assets	18,730	19,799
SWITZERLAND
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales to unaffiliated customers	2,709	3,131	4,130
Long-lived assets at July 31,
Long-lived assets	917	1,224
UNITED KINGDOM
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales to unaffiliated customers	1,730	1,904	2,023
Long-lived assets at July 31,
Long-lived assets	244	357
Other International Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales to unaffiliated customers	4,318	4,689	$ 5,405
Long-lived assets at July 31,
Long-lived assets	$ 197	$ 175