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@Ventures Investments - Additional information (Detail) (Co-venturer, USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended 3 Months Ended
Jan. 31, 2013
Oct. 31, 2012
Jan. 31, 2012
Jan. 31, 2013
Jan. 31, 2012
Jan. 31, 2013
Maximum
Jan. 31, 2013
Minimum
Jan. 31, 2013
Available For Sale Securities
Maximum
Jan. 31, 2013
Private Agreements
Jul. 31, 2012
Private Agreements
Investment In Unconsolidated Affiliates [Line Items]                    
Investments privately held companies $ 0.9   $ 1.1 $ 1.5 $ 1.1          
Carrying value of investment                 9.6 10.8
Impairment charges $ 1.5 $ 0 $ 0   $ 0          
Company's interest on Investment               20.00%    
Company's voting interest           50.00% 20.00%