Impairment Charges (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jan. 31, 2020 USD ($) ft²	Jan. 31, 2020 USD ($) ft²	Jan. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges	$ 10,057	$ 10,057	$ 0
Assets
Total assets held for sale	$ 10,680	$ 10,680		$ 0
Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of property (in sq ft) | ft²	400,000	400,000
Assets
Accounts receivable	$ 915	$ 915
Inventory	2,959	2,959
Property, plant and equipment	6,772	6,772
Other assets	34	34
Total assets held for sale	10,680	10,680
Liabilities
Accrued product warranties	556	556
Other accrued liabilities	131	131
Total liabilities held for sale	$ 687	$ 687