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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations, net of tax	$ (7,843)	$ 17,831	$ (27,375)	$ 25,453
Weighted-average shares outstanding - basic (in shares)	79,000	79,666	78,916	79,966
Dilutive effect of stock-based compensation (in shares)	0	1,444	0	1,783
Weighted-average shares outstanding - diluted (in shares)	79,000	81,110	78,916	81,749
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ (0.10)	$ 0.22	$ (0.35)	$ 0.32
Diluted (in dollars per share)	$ (0.10)	$ 0.22	$ (0.35)	$ 0.31