Variable Interest Entities- Investments, Equity Method and Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Apr. 08, 2021	Feb. 28, 2021	Oct. 01, 2019
Schedule of Equity Method Investments [Line Items]
Obligation to absorb risk of loss, percentage of partner's equity	100.00%			100.00%
Current assets	$ 777,532	$ 678,458		$ 777,532
Property, plant, and equipment, net	395,290	374,988		395,290
Goodwill	476,259	407,376		476,259
Intangible assets, net	328,024	290,075		328,024
Liabilities	(1,494,490)	(1,286,672)		(1,494,490)
Revenues	426,728		$ 346,564	792,996	$ 668,757
Operating Expenses	(110,586)		(90,151)	(208,316)	(169,485)
Operating profit (loss)	19,572		16,178	33,860	32,412
Purchase of outstanding equity	10,396	0		10,396
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Schedule of Equity Method Investments [Line Items]
Purchase of outstanding equity	$ 10,396	8,305		$ 10,396
Frontier
Schedule of Equity Method Investments [Line Items]
Percentage of voting interests acquired	68.00%			68.00%		8.00%		60.00%
Remaining percentage to be acquired	40.00%			40.00%				32.00%
Purchase of additional interest in subsidiaries		1,490
Frontier | Maximum
Schedule of Equity Method Investments [Line Items]
Remaining percentage to be acquired							10.00%
Treated Water Outsourcing
Schedule of Equity Method Investments [Line Items]
Partnership interest				50.00%
Cash	$ 1,165	1,380		$ 1,165
Current assets	3,195	3,202		3,195
Property, plant, and equipment, net	782	903		782
Goodwill	2,206	2,206		2,206
Liabilities	(791)	(1,009)		(791)
Revenues	796		834	1,641	1,668
Operating Expenses	(703)		(732)	(1,440)	(1,469)
Operating profit (loss)	93		102	201	199
Frontier
Schedule of Equity Method Investments [Line Items]
Cash	5,959	2,095		5,959
Current assets	13,278	12,495		13,278
Property, plant, and equipment, net	1,955	2,113		1,955
Goodwill	1,798	1,798		1,798
Intangible assets, net	7,439	8,265		7,439
Liabilities	(7,911)	$ (9,425)		(7,911)
Revenues	6,414		2,078	13,363	2,848
Operating Expenses	(6,149)		(2,401)	(12,135)	(4,139)
Operating profit (loss)	$ 265		$ (323)	$ 1,228	$ (1,291)