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, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations, net of tax	$ (8,782)	$ 10,474
Weighted-average shares outstanding - basic (in shares)	78,761	79,907
Dilutive effect of stock-based compensation (in shares)	0	1,746
Weighted-average shares outstanding - diluted (in shares)	78,761	81,653
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ (0.11)	$ 0.13
Diluted (in dollars per share)	$ (0.11)	$ 0.13