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, unless otherwise specified
12 Months Ended
Jul. 31, 2013
Jul. 31, 2012
Jul. 31, 2011
Allowance for doubtful accounts [Abstract]      
Beginning balance $ 3,273 $ 3,488  
Provision for doubtful accounts 4,496 5,104 4,431
Write-offs (5,062) (5,319)  
Ending balance $ 2,707 $ 3,273 $ 3,488