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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Income from continuing operations, net of tax	$ 17,831	$ 24,665	$ 25,453	$ 66,278
Weighted-average shares outstanding - basic (in shares)	79,666	80,950	79,966	80,821
Dilutive effect of stock-based compensation (in shares)	1,444	2,929	1,783	2,869
Weighted-average shares outstanding - diluted (in shares)	81,110	83,879	81,749	83,690
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ 0.22	$ 0.30	$ 0.32	$ 0.82
Diluted (in dollars per share)	$ 0.22	$ 0.29	$ 0.31	$ 0.79