Reconciliation of Basic and Diluted Shares - Reconciliation of Basic and Diluted Shares (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Income (loss) from continuing operations, net of tax	$ 1,462	$ (8,782)
Weighted-average shares outstanding - basic (in shares)	79,088	78,761
Dilutive effect of stock-based compensation (in shares)	927	0
Weighted-average shares outstanding - diluted (in shares)	80,015	78,761
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ 0.02	$ (0.11)
Diluted (in dollars per share)	$ 0.02	$ (0.11)