Summary of Significant Accounting Policies (Treated Water Outsourcing) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Subsidiary or Equity Method Investee [Line Items]
Current assets (includes cash of $3,903 and $3,304)	$ 637,293	$ 565,560
Property, plant and equipment	333,584	320,023
Goodwill	392,890	411,346	$ 321,913
Other non-current assets	25,715	23,842
Total liabilities	(1,372,026)	(1,301,601)
Total revenues	1,444,441	1,339,541	1,247,424
Total operating expenses	(371,249)	(345,702)	(332,048)
Income before interest expense and income taxes	59,672	66,846	69,204
Treated Water Outsourcing [Member]
Subsidiary or Equity Method Investee [Line Items]
Current assets (includes cash of $3,903 and $3,304)	6,324	5,486
Cash	3,903	3,304
Property, plant and equipment	2,186	4,441
Goodwill	2,206	2,206
Other non-current assets	3	3
Total liabilities	(2,388)	(3,608)
Total revenues	10,633	15,526	22,039
Total operating expenses	(8,732)	(12,996)	(14,835)
Income before interest expense and income taxes	$ 1,901	$ 2,530	$ 7,204