Revenue Recognition - Revenues by Primary Geographical Markets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 447,281	$ 350,898	$ 846,122	$ 680,800
Waste Processing and Reuse Solutions [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	161,579	0	240,391	0
Environmental services related to resource recovery for metals manufacturing and related logistical services
Disaggregation of Revenue [Line Items]
Total revenues	174,173	230,395	381,519	454,456
Applied Products [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	26,591	33,686	56,853	64,076
Aluminum Dross and Scrap Processing Systems [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	3,227	5,257	7,178	12,118
Railway Track Maintenance Equipment [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	40,411	38,960	83,026	72,568
After-market Parts and Services; Safety and Diagnostic Technology [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	32,500	36,700	63,700	68,001
Railway Contracting Services [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	8,800	5,900	13,455	9,581
North America
Disaggregation of Revenue [Line Items]
Total revenues	275,396	143,390	477,862	267,104
Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	99,827	109,016	214,308	217,250
Latin America
Disaggregation of Revenue [Line Items]
Total revenues	25,623	37,045	59,548	74,627
Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	27,774	40,750	55,638	82,509
Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	14,793	15,742	30,682	29,657
Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	3,868	4,955	8,084	9,653
Operating Segments | Harsco Environmental Segment
Disaggregation of Revenue [Line Items]
Total revenues	203,991	269,338	445,550	530,650
Operating Segments | Harsco Environmental Segment | Waste Processing and Reuse Solutions [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Environmental Segment | Environmental services related to resource recovery for metals manufacturing and related logistical services
Disaggregation of Revenue [Line Items]
Total revenues	174,173	230,395	381,519	454,456
Operating Segments | Harsco Environmental Segment | Applied Products [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	26,591	33,686	56,853	64,076
Operating Segments | Harsco Environmental Segment | Aluminum Dross and Scrap Processing Systems [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	3,227	5,257	7,178	12,118
Operating Segments | Harsco Environmental Segment | Railway Track Maintenance Equipment [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Environmental Segment | After-market Parts and Services; Safety and Diagnostic Technology [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Environmental Segment | Railway Contracting Services [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Environmental Segment | North America
Disaggregation of Revenue [Line Items]
Total revenues	57,356	78,112	127,237	151,461
Operating Segments | Harsco Environmental Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	82,972	98,478	179,289	196,699
Operating Segments | Harsco Environmental Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	25,108	36,272	58,368	73,263
Operating Segments | Harsco Environmental Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	19,894	35,779	41,890	69,917
Operating Segments | Harsco Environmental Segment | Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	14,793	15,742	30,682	29,657
Operating Segments | Harsco Environmental Segment | Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	3,868	4,955	8,084	9,653
Operating Segments | Harsco Clean Earth Segment
Disaggregation of Revenue [Line Items]
Total revenues	161,579	0	240,391	0
Operating Segments | Harsco Clean Earth Segment | Waste Processing and Reuse Solutions [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	161,579	0	240,391	0
Operating Segments | Harsco Clean Earth Segment | Environmental services related to resource recovery for metals manufacturing and related logistical services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Applied Products [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Aluminum Dross and Scrap Processing Systems [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Railway Track Maintenance Equipment [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | After-market Parts and Services; Safety and Diagnostic Technology [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Railway Contracting Services [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | North America
Disaggregation of Revenue [Line Items]
Total revenues	161,579	0	240,391	0
Operating Segments | Harsco Clean Earth Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment
Disaggregation of Revenue [Line Items]
Total revenues	81,711	81,560	160,181	150,150
Operating Segments | Harsco Rail Segment | Waste Processing and Reuse Solutions [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment | Environmental services related to resource recovery for metals manufacturing and related logistical services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment | Applied Products [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating Segments | Harsco Rail Segment | Aluminum Dross and Scrap Processing Systems [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment | Railway Track Maintenance Equipment [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	40,411	38,960	83,026	72,568
Operating Segments | Harsco Rail Segment | After-market Parts and Services; Safety and Diagnostic Technology [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	32,500	36,700	63,700	68,001
Operating Segments | Harsco Rail Segment | Railway Contracting Services [Domain]
Disaggregation of Revenue [Line Items]
Total revenues	8,800	5,900	13,455	9,581
Operating Segments | Harsco Rail Segment | North America
Disaggregation of Revenue [Line Items]
Total revenues	56,461	65,278	110,234	115,643
Operating Segments | Harsco Rail Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	16,855	10,538	35,019	20,551
Operating Segments | Harsco Rail Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	515	773	1,180	1,364
Operating Segments | Harsco Rail Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	7,880	4,971	13,748	12,592
Operating Segments | Harsco Rail Segment | Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment | Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 0	$ 0	$ 0