Annual report pursuant to Section 13 and 15(d)

Summary of significant accounting policies (Details) - Allowance for doubtful accounts

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Summary of significant accounting policies (Details) - Allowance for doubtful accounts - USD ($)
$ in Thousands
12 Months Ended
Jul. 31, 2018
Jul. 31, 2017
Jul. 31, 2016
Allowance for doubtful accounts [Abstract]      
Beginning balance $ 3,576 $ 3,517  
Provision for doubtful accounts 3,690 2,775 $ 2,336
Write-offs (4,598) (2,716)  
Ending balance $ 2,668 $ 3,576 $ 3,517