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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations, net of tax	$ (10,750)	$ (2,852)	$ (19,532)	$ 7,622
Weighted-average shares outstanding - basic (in shares)	78,987	80,328	78,874	80,119
Dilutive effect of stock-based compensation (in shares)	0	0	0	1,955
Weighted-average shares outstanding - diluted (in shares)	78,987	80,328	78,874	82,074
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ (0.14)	$ (0.04)	$ (0.25)	$ 0.10
Diluted (in dollars per share)	$ (0.14)	$ (0.04)	$ (0.25)	$ 0.09