Capital Stock (Details 2) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Common Stock
Common Stock, Shares, Issued	114,720,347	113,473,951	112,888,126
Treasury Stock, Shares, Beginning Balance	36,205,589	33,928,928	32,434,274
Common Stock, Shares, Outstanding, Beginning Balance	78,514,758	79,545,023	80,453,852
Vested Restricted Stock Units (in shares)	229,413	321,965	545,908
Stock Issued During Period, Shares, Other	471,412	908,566
Stock issued during period, stock appreciation rights (in shares)	8,870	15,865	39,917
Treasury shares purchased		1,766,826	1,321,072
Shares outstanding at the end of the period	115,430,042	114,720,347	113,473,951
Treasury Stock, Shares	36,505,672	36,205,589	33,928,928
Common Stock, Shares, Outstanding	78,924,370	78,514,758	79,545,023
Reconciliation of the average shares of common stock used to compute basic earnings per common share to the shares used to compute diluted earnings per common share
Income (loss) from continuing operations attributable to Harsco Corporation common stockholders (in dollars)	$ (32,526)	$ 28,231	$ 100,578
Weighted average shares of common stock outstanding	78,939,000	79,632,000	80,716,000
Dilutive effect of stock-based compensation (in shares)	0	1,743,000	2,879,000
Weighted-average shares outstanding—diluted (in shares)	78,939,000	81,375,000	83,595,000
Earnings (loss) from continuing operations per common share, attributable to Harsco Corporation common stockholders:
Basic (in dollars per share)	$ (0.41)	$ 0.35	$ 1.25
Income (Loss) from Continuing Operations, Per Diluted Share	$ (0.41)	$ 0.35	$ 1.20
Treasury Stock
Common Stock
Vested Restricted Stock Units (in shares)	91,188	125,863	161,774
Stock Issued During Period, Shares, Other	206,261	379,353
Stock issued during period, stock appreciation rights (in shares)	2,634	4,619	11,808
Treasury shares purchased		1,766,826	1,321,072
Outstanding Shares
Common Stock
Vested Restricted Stock Units (in shares)	138,225	196,102	384,134
Stock Issued During Period, Shares, Other	265,151	529,213
Stock issued during period, stock appreciation rights (in shares)	6,236	11,246	28,109
Treasury shares purchased		1,766,826	1,321,072