Acquisitions and Divestitures (Balance Sheet for Acquisitions 2018) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Goodwill	$ 392,890	$ 411,346	$ 321,913
Isotope
Business Acquisition [Line Items]
Current Assets		627
Property, plant and equipment		0
Goodwill		1,266
Intangible assets		933
Other non-current assets		0
Total asset acquired		2,826
Total liabilities assumed		(216)
Net assets acquired		2,610
ProAct
Business Acquisition [Line Items]
Current Assets		11,513
Property, plant and equipment		26,272
Goodwill		84,308
Intangible assets		27,464
Other non-current assets		0
Total asset acquired		149,557
Total liabilities assumed		(15,785)
Net assets acquired		133,772
Pacific Ozone
Business Acquisition [Line Items]
Current Assets		1,822
Property, plant and equipment		151
Goodwill		4,337
Intangible assets		2,678
Other non-current assets		135
Total asset acquired		9,123
Total liabilities assumed		(1,632)
Net assets acquired		7,491
Pure Water
Business Acquisition [Line Items]
Current Assets		295
Property, plant and equipment		156
Goodwill		2,506
Intangible assets		1,488
Other non-current assets		0
Total asset acquired		4,445
Total liabilities assumed		(278)
Net assets acquired		4,167
2018 Acquisitions
Business Acquisition [Line Items]
Current Assets		14,257
Property, plant and equipment		26,579
Goodwill		92,417
Intangible assets		32,563
Other non-current assets		135
Total asset acquired		165,951
Total liabilities assumed		(17,911)
Net assets acquired		$ 148,040