v3.26.1
Revenues - Narrative - New Enviri (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Total contract assets $ 75,200   $ 69,100
Total advances on contracts 9,100   8,200
Revenue recognized 4,700 $ 17,600  
New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Total contract assets 75,200   69,100
Total advances on contracts 9,100   $ 8,200
Revenue recognized $ 4,700 17,600  
SBB      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Percentage complete 91.00%    
(Decrease) to loss on contracts   1,100  
SBB | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Percentage complete 91.00%    
(Decrease) to loss on contracts   1,100  
Network Rail      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Provisions recognized $ 0 1,100  
Network Rail | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Provisions recognized $ 0 1,100  
Deutsche Bahn      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Percentage complete 56.00%    
Provisions recognized $ 0    
(Decrease) to loss on contracts   (13,300)  
Deutsche Bahn | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Percentage complete 56.00%    
Provisions recognized $ 0    
(Decrease) to loss on contracts   $ 13,300  
Contract | Network Rail      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Percentage complete 68.00%    
Contract | Network Rail | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Percentage complete 68.00%    
Harsco Environmental      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation $ 48,962    
Harsco Environmental | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 48,962    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 15,784    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 15,784    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 13,655    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 13,655    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 10,127    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 10,127    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,132    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,132    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,132    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,132    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,132    
Harsco Environmental | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,132    
Harsco Rail      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 108,990    
Harsco Rail | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 108,990    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 42,885    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 42,885    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 35,856    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 35,856    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 13,354    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 13,354    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 4,324    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 4,324    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,508    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 3,508    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-03-31      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation 9,063    
Harsco Rail | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-03-31 | New Enviri      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Remaining performance obligation $ 9,063