Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances	$ 789,659	$ 313,376	$ 215,165
OCI before reclassifications	(92,545)	(22,035)
Amounts reclassified from AOCI, net of tax	37,238	21,977
Total OCI	(55,307)	(58)	(21,505)
Less: OCI attributable to noncontrolling interests	(2,812)	972
OCI attributable to Harsco Corporation	(58,119)	914
Balances	713,399	789,659	313,376
Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		0	2,374
Balances			0
Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(588,536)
Balances			(588,536)
Cumulative Foreign Exchange Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances	(143,340)	(159,810)
OCI before reclassifications	7,854	17,261
Amounts reclassified from AOCI, net of tax	12,906	(1,763)
Total OCI	20,760	15,498
Less: OCI attributable to noncontrolling interests	(2,812)	972
OCI attributable to Harsco Corporation	17,948	16,470
Balances	(125,392)	(143,340)	(159,810)
Cumulative Foreign Exchange Translation Adjustments | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		0
Balances			0
Cumulative Foreign Exchange Translation Adjustments | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(159,810)
Balances			(159,810)
Effective Portion of Derivatives Designated as Hedging Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances	(3,717)	1,389
OCI before reclassifications	(3,709)	(7,050)
Amounts reclassified from AOCI, net of tax	1,586	1,944
Total OCI	(2,123)	(5,106)
Less: OCI attributable to noncontrolling interests	0	0
OCI attributable to Harsco Corporation	(2,123)	(5,106)
Balances	(5,840)	(3,717)	1,389
Effective Portion of Derivatives Designated as Hedging Instruments | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		0
Balances			0
Effective Portion of Derivatives Designated as Hedging Instruments | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		1,389
Balances			1,389
Cumulative Unrecognized Actuarial Losses on Pension Obligations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances	(440,562)	(408,655)
OCI before reclassifications	(96,684)	(32,274)
Amounts reclassified from AOCI, net of tax	22,746	21,796
Total OCI	(73,938)	(10,478)
Less: OCI attributable to noncontrolling interests	0	0
OCI attributable to Harsco Corporation	(73,938)	(10,478)
Balances	(514,500)	(440,562)	(408,655)
Cumulative Unrecognized Actuarial Losses on Pension Obligations | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(21,429)
Balances			(21,429)
Cumulative Unrecognized Actuarial Losses on Pension Obligations | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(430,084)
Balances			(430,084)
Unrealized Loss on Marketable Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances	(3)	(31)
OCI before reclassifications	(6)	28
Amounts reclassified from AOCI, net of tax	0	0
Total OCI	(6)	28
Less: OCI attributable to noncontrolling interests	0	0
OCI attributable to Harsco Corporation	(6)	28
Balances	(9)	(3)	(31)
Unrealized Loss on Marketable Securities | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		0
Balances			0
Unrealized Loss on Marketable Securities | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(31)
Balances			(31)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances	(587,622)	(567,107)	(546,582)
Total OCI	(58,119)	914	(19,005)
Balances	$ (645,741)	(587,622)	(567,107)
Total | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		$ (21,429)	(1,520)
Balances			$ (21,429)