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	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
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)	$ (163,542)	$ (125,736)	$ (79,161)
Weighted average shares of common stock outstanding	80,712	80,118	79,796
Dilutive effect of stock-based compensation (in shares)	0	0	0
Weighted-average shares outstanding—diluted (in shares)	80,712	80,118	79,796
Basic (in dollars per share)	$ (2.03)	$ (1.57)	$ (0.99)
Diluted (in dollars per share)	$ (2.03)	$ (1.57)	$ (0.99)