Commitments and Contingencies - Additional Information (Detail)	6 Months Ended
	Jan. 31, 2018 USD ($) Leases	Jul. 31, 2017 USD ($)
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Third-party claims for damages from company's product	$ 0	$ 0
Operating lease expiration year	2024
Number of lease extension options | Leases	1
Lease extension period	5 years
Lease termination notice period prior to expiration of original term	425 days
Purchase Commitment
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Non-cancelable inventory commitments	$ 64,500,000
Employee and Board of Director Member
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Claims for damages in connection with services	$ 0	$ 0