Acquisitions - Pure Water Solutions (Details)	Jan. 01, 2015 USD ($) project	Apr. 30, 2016 USD ($)	Jul. 31, 2015 USD ($)	Jul. 31, 2014 USD ($)
Net Assets
Goodwill		$ 284,018,000	$ 241,951,000	$ 231,647,000
Pure Water Solutions, Inc.
Acquisitions
Pre-acquisition annual revenues	$ 8,000,000
Total consideration for the transaction, excluding acquisition-related costs	11,835,000
Net Assets
Current assets	1,417,000
Property, plant and equipment	1,966,000
Other assets	20,000
Current liabilities	(503,000)
Net assets acquired	$ 8,870,000
Amortizable intangible assets, useful life	12 years
Number of in-process research and development projects acquired | project	0
Goodwill	$ 2,965,000
Goodwill deductible for income tax purposes	2,965,000
Pure Water Solutions, Inc. | Customer relationships
Net Assets
Amortizable intangible assets	$ 5,940,000
Amortizable intangible assets, useful life	12 years
Pure Water Solutions, Inc. | Brand names
Net Assets
Amortizable intangible assets	$ 30,000
Amortizable intangible assets, useful life	1 year