Revenue Recognition - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Revenue from Contract with Customer [Abstract]
Total contract assets	$ 60,100	$ 31,200
Revenue recognized in excess of amounts reclassified to trade accounts receivable, net	84,900	60,300
Contract with Customer, Liability, Revenue Recognized	75,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	1,863,864	1,503,742	$ 1,347,672
Contract estimated forward loss provision for Harsco Rail Segment			1,800	$ 45,100
Provision for Loss on Contracts	4,400	6,400
Revenues	1,863,864	1,503,742	1,347,672
SBB [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenues	$ 38,600	23,400	24,200
SBB [Member] | Contract 2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Percentage Complete	70.00%
Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	$ 84,100
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	24,800
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	19,800
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	14,200
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	13,700
Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	317,500
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	117,200
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	117,200
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	62,400
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	17,100
Waste Processing and Reuse Solutions [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	619,588	169,522
Railway Contracting Services [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	29,155	21,156	27,727
After-market Parts and Services; Safety and Diagnostic Technology [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	116,600	132,249	139,020
Aluminum Dross and Scrap Processing Systems [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	12,953	18,122	11,847
Railway Track Maintenance Equipment [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	184,076	145,968	112,547
General Corporate
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues			74
Environmental services related to resource recovery for metals manufacturing; and related logistical services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	781,060	888,850	927,969
Applied Products [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	120,432	127,875	128,488
Operating Segments [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	619,588	169,522	0
Revenues	619,588	169,522	0
Operating Segments [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	329,831	299,373	279,294
Revenues	329,831	299,373	279,294
Operating Segments [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	914,445	1,034,847	1,068,304
Revenues	914,445	1,034,847	1,068,304
Operating Segments [Member] | Waste Processing and Reuse Solutions [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	619,588	169,522
Operating Segments [Member] | Waste Processing and Reuse Solutions [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0
Operating Segments [Member] | Waste Processing and Reuse Solutions [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0
Operating Segments [Member] | Railway Contracting Services [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Railway Contracting Services [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	29,155	21,156	27,727
Operating Segments [Member] | Railway Contracting Services [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | After-market Parts and Services; Safety and Diagnostic Technology [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | After-market Parts and Services; Safety and Diagnostic Technology [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	116,600	132,249	139,020
Operating Segments [Member] | After-market Parts and Services; Safety and Diagnostic Technology [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Aluminum Dross and Scrap Processing Systems [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Aluminum Dross and Scrap Processing Systems [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Aluminum Dross and Scrap Processing Systems [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	12,953	18,122	11,847
Operating Segments [Member] | Railway Track Maintenance Equipment [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Railway Track Maintenance Equipment [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	184,076	145,968	112,547
Operating Segments [Member] | Railway Track Maintenance Equipment [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | General Corporate | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues			0
Operating Segments [Member] | Environmental services related to resource recovery for metals manufacturing; and related logistical services | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Environmental services related to resource recovery for metals manufacturing; and related logistical services | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Environmental services related to resource recovery for metals manufacturing; and related logistical services | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	781,060	888,850	927,969
Operating Segments [Member] | Applied Products [Member] | Clean Earth
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Applied Products [Member] | Harsco Rail
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Operating Segments [Member] | Applied Products [Member] | Harsco Environmental
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	120,432	127,875	128,488
Corporate
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	74
Revenues	0	0	74
Corporate | Waste Processing and Reuse Solutions [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0
Corporate | Railway Contracting Services [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Corporate | After-market Parts and Services; Safety and Diagnostic Technology [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Corporate | Aluminum Dross and Scrap Processing Systems [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Corporate | Railway Track Maintenance Equipment [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Corporate | General Corporate
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues			74
Corporate | Environmental services related to resource recovery for metals manufacturing; and related logistical services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	0	0	0
Corporate | Applied Products [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Product revenues	$ 0	$ 0	$ 0