Components of Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 716,583	$ 713,399	$ 758,870	$ 789,659	$ 713,399	$ 789,659
Other comprehensive income (loss) before reclassifications					6,465	(43,044)
Amounts reclassified from accumulated other comprehensive loss					12,677	26,073
Total other comprehensive income	17,913	1,229	13,031	(30,002)	19,142	(16,971)
Less: OCI attributable to noncontrolling interests					(393)	(975)
Other comprehensive income (loss) attributable to Harsco Corporation					19,535	(15,996)
Ending balance	749,383	716,583	764,516	758,870	749,383	764,516
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					12,150	(65,677)
Amounts reclassified from accumulated other comprehensive loss					0	12,906
Total other comprehensive income					12,150	(52,771)
Less: OCI attributable to noncontrolling interests					(393)	(975)
Other comprehensive income (loss) attributable to Harsco Corporation					12,543	(51,796)
Ending balance	(112,849)		(195,136)		(112,849)	(195,136)
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					(259)	(1,146)
Amounts reclassified from accumulated other comprehensive loss					1,182	(213)
Total other comprehensive income					923	(1,359)
Less: OCI attributable to noncontrolling interests					0	0
Other comprehensive income (loss) attributable to Harsco Corporation					923	(1,359)
Ending balance	(4,917)		(5,076)		(4,917)	(5,076)
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					(5,451)	23,810
Amounts reclassified from accumulated other comprehensive loss					11,495	13,380
Total other comprehensive income					6,044	37,190
Less: OCI attributable to noncontrolling interests					0	0
Other comprehensive income (loss) attributable to Harsco Corporation					6,044	37,190
Ending balance	(508,456)		(403,372)		(508,456)	(403,372)
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	(31)
Amounts reclassified from accumulated other comprehensive loss					0	0
Total other comprehensive income					25	(31)
Less: OCI attributable to noncontrolling interests					0	0
Other comprehensive income (loss) attributable to Harsco Corporation					25	(31)
Ending balance	16		(34)		16	(34)
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(643,446)	(645,741)	(616,476)	(587,622)	(645,741)	(587,622)
Total other comprehensive income	17,240	2,295	12,858	(28,854)
Ending balance	$ (626,206)	$ (643,446)	$ (603,618)	$ (616,476)	$ (626,206)	$ (603,618)