Acquisitions and Dispositions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Apr. 06, 2020
Business Acquisition [Line Items]
Goodwill	$ 900,314	$ 902,074
Gross Carrying Amount	523,318	523,048
Non-compete agreement
Business Acquisition [Line Items]
Gross Carrying Amount	2,500	2,500
Harsco Clean Earth Segment
Business Acquisition [Line Items]
Goodwill	483,879	$ 482,647
Harsco Clean Earth Segment | ESOL
Business Acquisition [Line Items]
Cash and cash equivalents	400		$ 400
Trade accounts receivable	122,600		124,100
Inventory	5,000		5,000
Other current assets	0		700
Property, plant and equipment	101,400		105,300
Right-of-use assets	56,000		56,000
Goodwill	153,300		152,000
Intangible assets	161,000		161,000
Other assets	200		200
Accounts payable	(50,100)		(48,600)
Accrued expenses	(19,300)		(17,500)
Current portion of operating lease liabilities	(16,600)		(16,600)
Other current liabilities	(6,600)		(6,400)
Environmental liabilities	(24,400)		(24,400)
Deferred income taxes	(17,000)		(15,500)
Operating lease liabilities	(39,400)		(39,400)
Total identifiable net assets of ESOL	426,500		436,300
Gross Carrying Amount	2,500		2,500
Business Acquisitions, Purchase Price Allocation	429,000		$ 438,800
Measurement Period Adjustments
Cash and cash equivalents	0
Trade accounts receivable	(1,500)
Inventory	0
Other current assets	(700)
Property, plant and equipment	(3,900)
Right-of-use assets	0
Goodwill	1,300
Intangible assets	0
Other assets	0
Accounts payable	(1,500)
Current portion of operating lease liabilities	(1,800)
Current portion of operating lease liabilities	0
Other current liabilities	(200)
Environmental liabilities	0
Deferred income taxes	(1,500)
Operating lease liabilities	0
Total identifiable net assets of ESOL	(9,800)
Total identifiable net assets of ESOL, including non-compete agreement	(9,800)
Harsco Clean Earth Segment | ESOL | Non-compete agreement
Measurement Period Adjustments
Intangible assets	$ 0