Capital Stock - Reconciliation of the average shares of common stock used to compute basic earnings per common share to the shares used to compute diluted earnings per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of the average shares of common stock used to compute basic earnings per common share to the shares used to compute diluted earnings per common share
Income (loss) from continuing operations attributable to Harsco Corporation common stockholders (in dollars)									$ 22,137	$ (49,727)	$ 10,311
Weighted average shares of common stock outstanding									79,234	78,939	79,632
Dilutive effect of stock-based compensation (in shares)									1,055	0	1,743
Weighted-average shares outstanding—diluted (in shares)									80,289	78,939	81,375
Basic (in dollars per share)	$ 0.13	$ 0.06	$ 0.11	$ (0.02)	$ (0.09)	$ (0.12)	$ (0.25)	$ (0.17)	$ 0.28	$ (0.63)	$ 0.13
Diluted (in dollars per share)	$ 0.13	$ 0.06	$ 0.11	$ (0.02)	$ (0.09)	$ (0.12)	$ (0.25)	$ (0.17)	$ 0.28	$ (0.63)	$ 0.13