Acquisitions and Dispositions - Acquisitions Narrative (Details) $ in Thousands, £ in Millions					1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 28, 2019 USD ($) facility	Jun. 28, 2019 USD ($) facility	Jun. 28, 2019 USD ($) facility TSDF_permits	Jun. 28, 2019 USD ($) facility RCRA_permits	May 31, 2018 GBP (£)	May 31, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	May 31, 2018 USD ($)
Business Acquisition [Line Items]
Total revenues							$ 423,155	$ 351,563	$ 1,103,955	$ 1,015,910
Additional interest expense							12,819	5,620	24,429	16,891
Purchase price									623,495	56,389
Harsco Clean Earth Segment
Business Acquisition [Line Items]
Percentage of interests acquired	100.00%	100.00%	100.00%	100.00%
Enterprise valuation		$ 625,000
Cash consideration		628,000
Post-closing period	5 years
Estimated reimbursements	$ 8,000	$ 8,000	$ 8,000	$ 8,000
Number of permitted facilities | facility	27	27	27	27
Number Of Permits Acquired			6	9
Goodwill to be deductible for income tax purposes	$ 16,300	$ 16,300	$ 16,300	$ 16,300
Direct acquisition costs							$ 2,000		14,500
Harsco Clean Earth Segment | Acquisition-related Borrowings
Business Acquisition [Line Items]
Additional interest expense								$ 9,100	$ 18,200	$ 27,000
Harsco Clean Earth Segment | Scenario, Forecast
Business Acquisition [Line Items]
Total revenues											$ 300,000
Altek
Business Acquisition [Line Items]
Cash consideration						$ 57,400
Estimated reimbursements												$ 12,100
Purchase price					£ 45	$ 60,000
Additional contingent consideration					£ 25							$ 33,000