Summary of significant accounting policies (Details) - Amount of expense related to share-based payment arrangements - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share Based Compensation	$ 939	$ 813	$ 831
Cost of Clinical Laboratory Services [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share Based Compensation			6
Selling, General and Administrative Expenses [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share Based Compensation	$ 939	$ 813	$ 825