Revenue Recognition - Remaining Performance Obligation (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Harsco Metals and Minerals
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	$ 98.7
Harsco Metals and Minerals | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	33.0
Period of expected timing of satisfaction		1 year
Harsco Metals and Minerals | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	19.6
Period of expected timing of satisfaction		1 year
Harsco Metals and Minerals | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	16.3
Period of expected timing of satisfaction		1 year
Harsco Metals and Minerals | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	12.8
Period of expected timing of satisfaction		1 year
Harsco Metals and Minerals | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Period of expected timing of satisfaction		1 year
Harsco Rail Segment
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	360.7
Harsco Rail Segment | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	126.0
Period of expected timing of satisfaction		1 year
Harsco Rail Segment | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	121.8
Period of expected timing of satisfaction		1 year
Harsco Rail Segment | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	55.2
Period of expected timing of satisfaction		1 year
Harsco Rail Segment | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	$ 46.5
Period of expected timing of satisfaction		1 year
Harsco Rail Segment | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Period of expected timing of satisfaction		1 year