Revenue Recognition - Revenues by Primary Geographical Markets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 544,301	$ 509,398	$ 1,642,976	$ 1,355,520
Waste Processing and Reuse Solutions
Disaggregation of Revenue [Line Items]
Total revenues	200,484	194,098	585,891	434,489
Environmental services related to resource recovery for metals manufacturing and related logistical services
Disaggregation of Revenue [Line Items]
Total revenues	230,340	181,867	688,923	563,701
Applied Products
Disaggregation of Revenue [Line Items]
Total revenues	36,091	38,166	100,706	95,019
Aluminum Dross and Scrap Processing Systems
Disaggregation of Revenue [Line Items]
Total revenues	3,470	2,474	10,804	9,337
Railway Track Maintenance Equipment
Disaggregation of Revenue [Line Items]
Total revenues	33,553	55,493	140,116	138,519
After-market Parts and Services; Safety and Diagnostic Technology
Disaggregation of Revenue [Line Items]
Total revenues	33,030	29,100	94,470	92,800
Railway Contracting Services
Disaggregation of Revenue [Line Items]
Total revenues	7,333	8,200	22,066	21,655
North America
Disaggregation of Revenue [Line Items]
Total revenues	320,516	315,876	980,098	793,738
Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	123,774	113,922	383,231	328,230
Latin America
Disaggregation of Revenue [Line Items]
Total revenues	35,765	29,497	101,345	89,045
Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	37,983	30,239	102,319	85,877
Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	20,804	15,558	60,798	46,240
Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	5,459	4,306	15,185	12,390
Operating Segments | Harsco Environmental Segment
Disaggregation of Revenue [Line Items]
Total revenues	269,901	222,507	800,433	668,057
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	230,340	181,867	688,923	563,701
Operating Segments | Harsco Environmental Segment | Applied Products
Disaggregation of Revenue [Line Items]
Total revenues	36,091	38,166	100,706	95,019
Operating Segments | Harsco Environmental Segment | Aluminum Dross and Scrap Processing Systems
Disaggregation of Revenue [Line Items]
Total revenues	3,470	2,474	10,804	9,337
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	71,479	58,973	208,395	186,210
Operating Segments | Harsco Environmental Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	106,859	92,506	336,011	271,795
Operating Segments | Harsco Environmental Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	35,072	29,085	99,524	87,453
Operating Segments | Harsco Environmental Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	30,228	22,079	80,520	63,969
Operating Segments | Harsco Environmental Segment | Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	20,804	15,558	60,798	46,240
Operating Segments | Harsco Environmental Segment | Eastern Europe
Disaggregation of Revenue [Line Items]
Total revenues	5,459	4,306	15,185	12,390
Operating Segments | Harsco Clean Earth Segment
Disaggregation of Revenue [Line Items]
Total revenues	200,484	194,098	585,891	434,489
Operating Segments | Harsco Clean Earth Segment | Waste Processing and Reuse Solutions
Disaggregation of Revenue [Line Items]
Total revenues	200,484	194,098	585,891	434,489
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	200,484	194,098	585,891	434,489
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	73,916	92,793	256,652	252,974
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	33,553	55,493	140,116	138,519
Operating Segments | Harsco Rail Segment | After-market Parts and Services; Safety and Diagnostic Technology
Disaggregation of Revenue [Line Items]
Total revenues	33,030	29,100	94,470	92,800
Operating Segments | Harsco Rail Segment | Railway Contracting Services
Disaggregation of Revenue [Line Items]
Total revenues	7,333	8,200	22,066	21,655
Operating Segments | Harsco Rail Segment | North America
Disaggregation of Revenue [Line Items]
Total revenues	48,553	62,805	185,812	173,039
Operating Segments | Harsco Rail Segment | Western Europe
Disaggregation of Revenue [Line Items]
Total revenues	16,915	21,416	47,220	56,435
Operating Segments | Harsco Rail Segment | Latin America
Disaggregation of Revenue [Line Items]
Total revenues	693	412	1,821	1,592
Operating Segments | Harsco Rail Segment | Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenues	7,755	8,160	21,799	21,908
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