Acquisitions and Dispositions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2020	Apr. 06, 2020	Dec. 31, 2019	Jun. 28, 2019
Business Acquisition [Line Items]
Goodwill			$ 881,911		$ 738,369
Gross Carrying Amount			517,059		412,657
Noncompete Agreements
Business Acquisition [Line Items]
Gross Carrying Amount			2,500		0
Harsco Clean Earth Segment
Business Acquisition [Line Items]
Cash and cash equivalents			3,600
Trade accounts receivable, net			62,500
Other receivables			2,100
Other current assets			7,300
Property, plant and equipment			77,000
Right-of-use assets			25,800
Goodwill			330,600
Intangible assets			242,200			$ 261,100
Other assets			1,200
Accounts payable			(23,100)
Other current liabilities			(19,700)
Deferred income taxes			45,700
Operating lease liabilities			(19,500)
Total identifiable net assets of Clean Earth			635,700			635,900
Acquisition consideration payable (b)			0
Other liabilities			(8,600)
Harsco Clean Earth Segment
Business Acquisition [Line Items]
Goodwill			474,513		$ 330,230
Measurement Period Adjustments
Intangible assets		$ (18,900)
Total identifiable intangible assets of Clean Earth		200
Harsco Clean Earth Segment | ESOL
Business Acquisition [Line Items]
Cash and cash equivalents			400	$ 400
Trade accounts receivable, net			123,200	124,100
Inventory			5,000	5,000
Other current assets			300	700
Property, plant and equipment			105,300	105,300
Right-of-use assets			56,000	56,000
Goodwill			143,900	152,000
Intangible assets			161,000	161,000
Other assets			200	200
Accounts payable			(49,000)	(48,600)
Accrued expenses			17,500	17,500
Current portion of operating lease liabilities			16,600	16,600
Other current liabilities			(6,400)	(6,400)
Environmental liabilities			24,400	24,400
Deferred income taxes			15,500	15,500
Operating lease liabilities			(39,400)	(39,400)
Total identifiable net assets of Clean Earth			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	(900)
Inventory	0
Other current assets	(400)
Property, plant and equipment	0
Right-of-use assets	0
Goodwill	(8,100)
Intangible assets	0
Other assets	0
Accounts payable	(400)
Current portion of operating lease liabilities	0
Current portion of operating lease liabilities	0
Other current liabilities	0
Environmental liabilities	0
Deferred income taxes	0
Operating lease liabilities	0
Total identifiable intangible assets of Clean Earth	9,800
Total identifiable net assets of ESOL, including non-compete agreement	(9,800)
Harsco Clean Earth Segment | ESOL | Noncompete Agreements
Measurement Period Adjustments
Intangible assets	$ 0
Harsco Clean Earth Segment | Harsco Clean Earth Segment
Business Acquisition [Line Items]
Cash and cash equivalents						42,800
Trade accounts receivable, net						63,700
Other receivables						800
Other current assets						8,700
Property, plant and equipment						75,600
Right-of-use assets						14,400
Goodwill						313,800
Intangible assets						261,100
Other assets						4,000
Accounts payable						(23,000)
Other current liabilities						(18,000)
Deferred income taxes						51,200
Operating lease liabilities						(11,100)
Acquisition consideration payable (b)						(39,200)
Other liabilities						$ (6,500)
Measurement Period Adjustments
Cash and cash equivalents		(39,200)
Trade accounts receivable		(1,200)
Other current assets		(1,400)
Property, plant and equipment		1,400
Right-of-use assets		11,400
Goodwill		16,800
Intangible assets		(18,900)
Other assets		(2,800)
Accounts payable		(100)
Other current liabilities		(1,700)
Deferred income taxes		5,500
Operating lease liabilities		(8,400)
Other receivables		1,300
Acquisition consideration payable (b)		39,200
Other liabilities		$ (2,100)