Annual report pursuant to Section 13 and 15(d)

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

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Summary of significant accounting policies (Detail) - Allowance for doubtful accounts (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Jul. 31, 2012
Jul. 31, 2011
Jul. 31, 2010
Beginning balance $ 3,488 $ 2,839  
Provision for doubtful accounts 5,104 4,431 3,480
Write-offs (5,319) (3,782)  
Ending balance $ 3,273 $ 3,488 $ 2,839