Components of Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 713,399	$ 789,659
Other comprehensive income (loss) before reclassifications	(5,057)	(51,103)
Amounts reclassified from accumulated other comprehensive loss	6,286	21,101
Total other comprehensive income (loss)	1,229	(30,002)
OCI attributable to noncontrolling interests	1,066	1,148
Other comprehensive income (loss) attributable to Harsco Corporation	2,295	(28,854)
Ending balance	716,583	758,870
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(125,392)	(143,340)
Other comprehensive income (loss) before reclassifications	(3,296)	(71,472)
Amounts reclassified from accumulated other comprehensive loss	0	12,906
Total other comprehensive income (loss)	(3,296)	(58,566)
OCI attributable to noncontrolling interests	1,066	1,148
Other comprehensive income (loss) attributable to Harsco Corporation	(2,230)	(57,418)
Ending balance	(127,622)	(200,758)
Effective Portion of Deriviatives Designated as Hedging Instruments
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(5,840)	(3,717)
Other comprehensive income (loss) before reclassifications	119	(1,042)
Amounts reclassified from accumulated other comprehensive loss	570	(645)
Total other comprehensive income (loss)	689	(1,687)
OCI attributable to noncontrolling interests	0	0
Other comprehensive income (loss) attributable to Harsco Corporation	689	(1,687)
Ending balance	(5,151)	(5,404)
Cumulative Unrecognized Actuarial Losses on Pension Obligations
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(514,500)	(440,562)
Other comprehensive income (loss) before reclassifications	(1,897)	21,429
Amounts reclassified from accumulated other comprehensive loss	5,716	8,840
Total other comprehensive income (loss)	3,819	30,269
OCI attributable to noncontrolling interests	0	0
Other comprehensive income (loss) attributable to Harsco Corporation	3,819	30,269
Ending balance	(510,681)	(410,293)
Unrealized Loss on Marketable Securities
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(9)	(3)
Other comprehensive income (loss) before reclassifications	17	(18)
Amounts reclassified from accumulated other comprehensive loss	0	0
Total other comprehensive income (loss)	17	(18)
OCI attributable to noncontrolling interests	0	0
Other comprehensive income (loss) attributable to Harsco Corporation	17	(18)
Ending balance	8	(21)
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(645,741)	(587,622)
Total other comprehensive income (loss)	2,295	(28,854)
Ending balance	$ (643,446)	$ (616,476)