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Fair value Measurement of Assets and Liabilities - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Jan. 31, 2017
Jul. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Defined benefit plans assets percentage invested in bank-managed portfolios 100.00%  
Fair value, assets, Level 1 to Level 2 transfers, amount $ 0 $ 0
Fair value, assets, Level 2 to Level 1 transfers, amount 0 0
Fair value, assets, transfers into Level 3 0 0
Fair value, assets, transfers out of Level 3 $ 0 $ 0