Summary of Net Accounts Receivable Greater than or Equal to 10% of Net Account Receivable Balance (Detail) (Accounts Receivable, Credit Concentration Risk) (Parenthetical) (Detail) - Accounts Receivable - Largest customers - Maximum	3 Months Ended	12 Months Ended
	Oct. 31, 2017	Jul. 31, 2017
GE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of net accounts receivable	10.00%
Smiths Detection
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of net accounts receivable		10.00%