Components of Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 749,383	$ 716,583	$ 713,399	$ 764,516	$ 758,870	$ 789,659	$ 713,399	$ 789,659
Other comprehensive income (loss) before reclassifications							(8,527)	(40,493)
Amounts reclassified from accumulated other comprehensive loss							18,672	31,642
Total other comprehensive income (loss)	(8,997)	17,913	1,229	8,120	13,031	(30,002)	10,145	(8,851)
Less: OCI attributable to noncontrolling interests							(837)	579
Other comprehensive income (loss) attributable to Harsco Corporation							10,982	(9,430)
Ending balance	753,227	749,383	716,583	766,414	764,516	758,870	753,227	766,414
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(125,392)			(143,340)	(125,392)	(143,340)
Other comprehensive income (loss) before reclassifications							(15,437)	(48,150)
Amounts reclassified from accumulated other comprehensive loss							0	12,906
Total other comprehensive income (loss)							(15,437)	(35,244)
Less: OCI attributable to noncontrolling interests							(837)	579
Other comprehensive income (loss) attributable to Harsco Corporation							(14,600)	(35,823)
Ending balance	(139,992)			(179,163)			(139,992)	(179,163)
Effective Portion of Deriviatives Designated as Hedging Instruments
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(5,840)			(3,717)	(5,840)	(3,717)
Other comprehensive income (loss) before reclassifications							257	(2,226)
Amounts reclassified from accumulated other comprehensive loss							1,488	604
Total other comprehensive income (loss)							1,745	(1,622)
Less: OCI attributable to noncontrolling interests							0	0
Other comprehensive income (loss) attributable to Harsco Corporation							1,745	(1,622)
Ending balance	(4,095)			(5,339)			(4,095)	(5,339)
Cumulative Unrecognized Actuarial Losses on Pension Obligations
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(514,500)			(440,562)	(514,500)	(440,562)
Other comprehensive income (loss) before reclassifications							6,628	9,905
Amounts reclassified from accumulated other comprehensive loss							17,184	18,132
Total other comprehensive income (loss)							23,812	28,037
Less: OCI attributable to noncontrolling interests							0	0
Other comprehensive income (loss) attributable to Harsco Corporation							23,812	28,037
Ending balance	(490,688)			(412,525)			(490,688)	(412,525)
Unrealized Loss on Marketable Securities
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(9)			(3)	(9)	(3)
Other comprehensive income (loss) before reclassifications							25	(22)
Amounts reclassified from accumulated other comprehensive loss							0	0
Total other comprehensive income (loss)							25	(22)
Less: OCI attributable to noncontrolling interests							0	0
Other comprehensive income (loss) attributable to Harsco Corporation							25	(22)
Ending balance	16			(25)			16	(25)
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(626,206)	(643,446)	(645,741)	(603,618)	(616,476)	(587,622)	(645,741)	(587,622)
Total other comprehensive income (loss)	(8,553)	17,240	2,295	6,566	12,858	(28,854)
Ending balance	$ (634,759)	$ (626,206)	$ (643,446)	$ (597,052)	$ (603,618)	$ (616,476)	$ (634,759)	$ (597,052)