Acquisitions and Dispositions - Summary of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	9 Months Ended		18 Months Ended
	Dec. 31, 2020	Mar. 31, 2019	Dec. 31, 2020	Apr. 06, 2020	Dec. 31, 2019	Jun. 28, 2019	Dec. 31, 2018	Jun. 30, 2018
Final Valuation
Goodwill	$ 902,074		$ 902,074		$ 738,369		$ 404,713
Non-compete agreement	523,048		523,048		412,657
Clean Earth
Final Valuation
Intangible assets	242,200		242,200			$ 261,100
Altek
Final Valuation
Cash and cash equivalents		$ 1,700						$ 1,700
Property, plant and equipment		3,300						3,300
Goodwill		22,500						20,900
Intangible assets		52,700						52,500
Net deferred tax liabilities		(8,500)						(8,500)
Net working capital		(1,300)						(1,500)
Other liabilities		(300)						(300)
Total identifiable net assets		70,100						$ 68,100
Measurement Period Adjustments
Measurement period adjustment, net working capital		200
Measurement period adjustment, intangible assets		200
Measurement period adjustment, goodwill		1,600
Total identifiable net assets		$ 2,000
Clean Earth
Final Valuation
Goodwill	482,647		482,647		$ 330,230		$ 0
Measurement Period Adjustments
Measurement period adjustment, intangible assets			(18,900)
Clean Earth | Clean Earth
Final Valuation
Cash and cash equivalents	3,600		3,600			42,800
Trade accounts receivable, net	62,500		62,500			63,700
Other current assets	7,300		7,300			8,700
Property, plant and equipment	77,000		77,000			75,600
Right-of-use assets	25,800		25,800			14,400
Goodwill	330,600		330,600			313,800
Intangible assets	242,200		242,200			261,100
Other assets	1,200		1,200			4,000
Accounts payable	(23,100)		(23,100)			(23,000)
Other current liabilities	(19,700)		(19,700)			(18,000)
Net deferred tax liabilities	(45,700)		(45,700)			(51,200)
Operating lease liabilities	(19,500)		(19,500)			(11,100)
Other receivables	2,100		2,100			800
Acquisition consideration payable (b)	0		0			(39,200)
Other liabilities	(8,600)		(8,600)			(6,500)
Total identifiable net assets	635,700		635,700			$ 635,900
Measurement Period Adjustments
Measurement period adjustment, cash and cash equivalent			(39,200)
Measurement period adjustment, trade accounts receivable, net			(1,200)
Measurement period adjustment, other receivable			1,300
Measurement period adjustment, other current assets			(1,400)
Measurement period adjustment, property, plant and equipment			1,400
Measurement period adjustment, right-of-use assets			11,400
Measurement period adjustment, other assets			(2,800)
Measurement period adjustment, acquisition consideration payable			39,200
Measurement period adjustment, other current liabilities			(1,700)
Measurement period adjustment, accounts payable			100
Measurement period adjustment, deferred income taxes			5,500
Measurement period adjustment, operating lease liabilities			(8,400)
Measurement period adjustment, other liabilities			(2,100)
Measurement period adjustment, intangible assets			(18,900)
Measurement period adjustment, goodwill			16,800
Total identifiable net assets			(200)
Clean Earth | ESOL
Final Valuation
Cash and cash equivalents	400		400	$ 400
Trade accounts receivable, net	122,900		122,900	124,100
Inventory	5,000		5,000	5,000
Other current assets	300		300	700
Property, plant and equipment	102,200		102,200	105,300
Right-of-use assets	56,000		56,000	56,000
Goodwill	152,100		152,100	152,000
Intangible assets	161,000		161,000	161,000
Other assets	200		200	200
Accounts payable	(50,100)		(50,100)	(48,600)
Accrued expenses	(19,500)		(19,500)	(17,500)
Current portion of operating lease liabilities	(16,600)		(16,600)	(16,600)
Other current liabilities	(6,400)		(6,400)	(6,400)
Environmental liabilities	(24,400)		(24,400)	(24,400)
Net deferred tax liabilities	(17,200)		(17,200)	(15,500)
Operating lease liabilities	(39,400)		(39,400)	(39,400)
Non-compete agreement	2,500		2,500	2,500
Total identifiable net assets	426,500		426,500	436,300
Business Acquisitions, Purchase Price Allocation	429,000		$ 429,000	$ 438,800
Measurement Period Adjustments
Measurement period adjustment, cash and cash equivalent	0
Measurement period adjustment, trade accounts receivable, net	(1,200)
Measurement period adjustment, environmental liabilities	0
Measurement period adjustment, other current assets	(400)
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Purchase Price Allocation	(9,800)
Measurement period adjustment, current portion of operating lease liabilities	0
Measurement period adjustment, property, plant and equipment	(3,100)
Measurement period adjustment, right-of-use assets	0
Measurement period adjustment, inventory	0
Measurement period adjustment, other assets	0
Measurement period adjustment, other current liabilities	0
Measurement period adjustment, accrued expenses	(2,000)
Measurement period adjustment, accounts payable	1,500
Measurement period adjustment, deferred income taxes	(1,700)
Measurement period adjustment, operating lease liabilities	0
Measurement period adjustment, intangible assets	0
Measurement period adjustment, goodwill	100
Total identifiable net assets	$ (9,800)