Summary of Net Accounts Receivable Greater than or Equal to 10% of Net Account Receivable Balance (Detail) (Accounts Receivable, Credit Concentration Risk) (Detail) - Accounts Receivable - Credit Concentration Risk	6 Months Ended	12 Months Ended
	Jan. 31, 2018	Jul. 31, 2017
GE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of net accounts receivable		11.00%
Philips
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of net accounts receivable	16.00%	14.00%
Smiths Detection
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of net accounts receivable	10.00%