Acquisitions and Divestitures - Balance Sheet for Acquisitions (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Goodwill	$ 324,272	$ 321,913
Pure Water Solutions [Member]
Business Acquisition [Line Items]
Current assets	277
Property, plant and equipment	175
Goodwill	2,462
Intangible assets	1,488
Total assets acquired	4,402
Total liabilities assumed	(164)
Net assets acquired	4,238
Pacific Ozone [Member]
Business Acquisition [Line Items]
Current assets	1,953
Property, plant and equipment	151
Goodwill	3,757
Intangible assets	2,678
Total assets acquired	8,539
Total liabilities assumed	(916)
Net assets acquired	7,623
2018 Acquisitions [Member]
Business Acquisition [Line Items]
Current assets	2,230
Property, plant and equipment	326
Goodwill	6,219
Intangible assets	4,166
Total assets acquired	12,941
Total liabilities assumed	(1,080)
Net assets acquired	$ 11,861