Revenue Recognition - Revenues by Primary Geographical Markets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 569,820	$ 447,281	$ 1,098,675	$ 846,122
Waste Processing and Reuse Solutions
Disaggregation of Revenue [Line Items]
Total revenues	196,128	161,579	385,407	240,391
Environmental services related to resource recovery for metals manufacturing and related logistical services
Disaggregation of Revenue [Line Items]
Total revenues	233,523	174,238	458,583	381,834
Applied Products
Disaggregation of Revenue [Line Items]
Total revenues	34,830	26,591	64,615	56,853
Aluminum Dross and Scrap Processing Systems
Disaggregation of Revenue [Line Items]
Total revenues	4,193	3,162	7,334	6,863
Railway Track Maintenance Equipment
Disaggregation of Revenue [Line Items]
Total revenues	60,123	40,411	106,563	83,026
After-market Parts and Services; Safety and Diagnostic Technology
Disaggregation of Revenue [Line Items]
Total revenues	34,671	32,500	61,440	63,700
Railway Contracting Services
Disaggregation of Revenue [Line Items]
Total revenues	6,352	8,800	14,733	13,455
North America
Disaggregation of Revenue [Line Items]
Total revenues	344,861	275,396	659,582	477,862
Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	130,653	99,827	259,457	214,308
Latin America
Disaggregation of Revenue [Line Items]
Total revenues	34,367	25,623	65,580	59,548
Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	34,830	27,774	64,336	55,638
Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	19,873	14,793	39,994	30,682
Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	5,236	3,868	9,726	8,084
Operating Segments | Harsco Environmental Segment
Disaggregation of Revenue [Line Items]
Total revenues	272,546	203,991	530,532	445,550
Operating Segments | Harsco Environmental Segment | Waste Processing and Reuse Solutions
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	233,523	174,238	458,583	381,834
Operating Segments | Harsco Environmental Segment | Applied Products
Disaggregation of Revenue [Line Items]
Total revenues	34,830	26,591	64,615	56,853
Operating Segments | Harsco Environmental Segment | Aluminum Dross and Scrap Processing Systems
Disaggregation of Revenue [Line Items]
Total revenues	4,193	3,162	7,334	6,863
Operating Segments | Harsco Environmental Segment | Railway Track Maintenance Equipment
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
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Environmental Segment | Railway Contracting Services
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	69,735	57,356	136,916	127,237
Operating Segments | Harsco Environmental Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	116,981	82,972	229,152	179,289
Operating Segments | Harsco Environmental Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	33,799	25,108	64,452	58,368
Operating Segments | Harsco Environmental Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	26,922	19,894	50,292	41,890
Operating Segments | Harsco Environmental Segment | Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	19,873	14,793	39,994	30,682
Operating Segments | Harsco Environmental Segment | Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	5,236	3,868	9,726	8,084
Operating Segments | Harsco Clean Earth Segment
Disaggregation of Revenue [Line Items]
Total revenues	196,128	161,579	385,407	240,391
Operating Segments | Harsco Clean Earth Segment | Waste Processing and Reuse Solutions
Disaggregation of Revenue [Line Items]
Total revenues	196,128	161,579	385,407	240,391
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
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Aluminum Dross and Scrap Processing Systems
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Railway Track Maintenance Equipment
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
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Clean Earth Segment | Railway Contracting Services
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	196,128	161,579	385,407	240,391
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	101,146	81,711	182,736	160,181
Operating Segments | Harsco Rail Segment | Waste Processing and Reuse Solutions
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
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment | Aluminum Dross and Scrap Processing Systems
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Harsco Rail Segment | Railway Track Maintenance Equipment
Disaggregation of Revenue [Line Items]
Total revenues	60,123	40,411	106,563	83,026
Operating Segments | Harsco Rail Segment | After-market Parts and Services; Safety and Diagnostic Technology
Disaggregation of Revenue [Line Items]
Total revenues	34,671	32,500	61,440	63,700
Operating Segments | Harsco Rail Segment | Railway Contracting Services
Disaggregation of Revenue [Line Items]
Total revenues	6,352	8,800	14,733	13,455
Operating Segments | Harsco Rail Segment | North America
Disaggregation of Revenue [Line Items]
Total revenues	78,998	56,461	137,259	110,234
Operating Segments | Harsco Rail Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	13,672	16,855	30,305	35,019
Operating Segments | Harsco Rail Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	568	515	1,128	1,180
Operating Segments | Harsco Rail Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	7,908	7,880	14,044	13,748
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