Acquisitions and Divestitures (WCSI Acquisition) (Details) - USD ($) $ in Thousands		12 Months Ended
	Apr. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Cash paid to acquire assets		$ 21,037	$ 13,108	$ 2,873
Goodwill		407,376	$ 397,205	$ 392,890
Water consulting specialists, inc
Business Acquisition [Line Items]
Cash paid to acquire assets	$ 12,025
Contingent consideration, liability	761	150
Proceeds from Previous Acquisition		21
Business Acquisition, Transaction Costs		$ 83
Current assets	1,813
Property, plant, and equipment	221
Goodwill	4,340
Intangible assets	7,336
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets	86
Total assets acquired	13,796
Other liabilities assumed	(1,792)
Net assets acquired	$ 12,004