Components of Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Jan. 01, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Adoption of new accounting standard									$ 0
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 764,516	$ 758,870	$ 789,659	$ 349,114	$ 335,272	$ 313,376	$ 789,659	$ 313,376
Other comprehensive income (loss) before reclassifications							(40,493)	(14,753)
Amounts reclassified from accumulated other comprehensive loss							31,642	13,662
Total other comprehensive income (loss)	8,120	13,031	(30,002)	(9,220)	3,598	4,531	(8,851)	(1,091)
OCI attributable to noncontrolling interests							(579)	1,868
Other comprehensive income (loss) attributable to Harsco Corporation							(9,430)	777
Ending balance	766,414	764,516	758,870	751,260	349,114	335,272	766,414	751,260
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(143,340)			(159,810)	(143,340)	(159,810)
Other comprehensive income (loss) before reclassifications							(48,150)	(20,513)
Amounts reclassified from accumulated other comprehensive loss							12,906	(1,763)
Total other comprehensive income (loss)							(35,244)	(22,276)
OCI attributable to noncontrolling interests							(579)	1,868
Other comprehensive income (loss) attributable to Harsco Corporation							(35,823)	(20,408)
Ending balance	(179,163)			(180,218)			(179,163)	(180,218)
Effective Portion of Deriviatives Designated as Hedging Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Adoption of new accounting standard									0
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(3,717)			1,389	(3,717)	1,389
Other comprehensive income (loss) before reclassifications							(2,226)	(5,889)
Amounts reclassified from accumulated other comprehensive loss							604	1,404
Total other comprehensive income (loss)							(1,622)	(4,485)
OCI attributable to noncontrolling interests							0	0
Other comprehensive income (loss) attributable to Harsco Corporation							(1,622)	(4,485)
Ending balance	(5,339)			(3,096)			(5,339)	(3,096)
Cumulative Unrecognized Actuarial Losses on Pension Obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Adoption of new accounting standard									(21,429)
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(440,562)			(408,655)	(440,562)	(408,655)
Other comprehensive income (loss) before reclassifications							9,905	11,630
Amounts reclassified from accumulated other comprehensive loss							18,132	14,021
Total other comprehensive income (loss)							28,037	25,651
OCI attributable to noncontrolling interests							0	0
Other comprehensive income (loss) attributable to Harsco Corporation							28,037	25,651
Ending balance	(412,525)			(404,433)			(412,525)	(404,433)
Unrealized Loss on Marketable Securities
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(3)			(31)	(3)	(31)
Other comprehensive income (loss) before reclassifications							(22)	19
Amounts reclassified from accumulated other comprehensive loss							0	0
Total other comprehensive income (loss)							(22)	19
OCI attributable to noncontrolling interests							0	0
Other comprehensive income (loss) attributable to Harsco Corporation							(22)	19
Ending balance	(25)			(12)			(25)	(12)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Adoption of new accounting standard									$ (21,429)
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(603,618)	(616,476)	(587,622)	(580,229)	(584,425)	(567,107)	(587,622)	(567,107)
Total other comprehensive income (loss)	6,566	12,858	(28,854)	(7,530)	4,196	4,111
Ending balance	$ (597,052)	$ (603,618)	$ (616,476)	$ (587,759)	$ (580,229)	$ (584,425)	$ (597,052)	$ (587,759)