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, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Income from continuing operations, net of tax	$ 21,029	$ 18,260
Weighted-average shares outstanding - basic (in shares)	79,907	80,650
Dilutive effect of stock-based compensation (in shares)	1,746	2,894
Weighted-average shares outstanding - diluted (in shares)	81,653	83,544
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ 0.26	$ 0.23
Diluted (in dollars per share)	$ 0.26	$ 0.22