Components of Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			$ 215,165	$ 137,563
Accumulated other comprehensive loss					$ (2,375)		$ (397)
Other comprehensive income (loss) before reclassifications			(24,151)	11,935
Amounts reclassified from accumulated other comprehensive loss			14,350	15,471
Total other comprehensive income	$ 1,225	$ 10,885	(9,801)	27,406
Other comprehensive loss attributable to noncontrolling interests			2,612	(2,235)
Other comprehensive income (loss) attributable to Harsco Corporation			(7,189)	25,171
Balances	304,391	210,018	304,391	210,018
Cumulative Foreign Exchange Translation Adjustments
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			(111,567)	(144,534)
Other comprehensive income (loss) before reclassifications			(40,157)	42,391
Amounts reclassified from accumulated other comprehensive loss			0	0
Total other comprehensive income			(40,157)	42,391
Other comprehensive loss attributable to noncontrolling interests			2,612	(2,235)
Other comprehensive income (loss) attributable to Harsco Corporation			(37,545)	40,156
Balances	(149,112)	(104,378)	(149,112)	(104,378)
Effective Portion of Deriviatives Designated as Hedging Instruments
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			808	(1,089)
Other comprehensive income (loss) before reclassifications			6,055	1,133
Amounts reclassified from accumulated other comprehensive loss			26	338
Total other comprehensive income			6,081	1,471
Other comprehensive loss attributable to noncontrolling interests			0	0
Other comprehensive income (loss) attributable to Harsco Corporation			6,081	1,471
Balances	5,369	382	5,369	382
Cumulative Unrecognized Actuarial Losses on Pension Obligations
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			(435,840)	(461,094)
Other comprehensive income (loss) before reclassifications			9,970	(31,600)
Amounts reclassified from accumulated other comprehensive loss			14,324	15,133
Total other comprehensive income			24,294	(16,467)
Other comprehensive loss attributable to noncontrolling interests			0	0
Other comprehensive income (loss) attributable to Harsco Corporation			24,294	(16,467)
Balances	(411,546)	(477,561)	(411,546)	(477,561)
Unrealized Loss on Marketable Securities
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			17	(5)
Other comprehensive income (loss) before reclassifications			(19)	11
Amounts reclassified from accumulated other comprehensive loss			0	0
Total other comprehensive income			(19)	11
Other comprehensive loss attributable to noncontrolling interests			0	0
Other comprehensive income (loss) attributable to Harsco Corporation			(19)	11
Balances	(2)	6	(2)	6
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			(546,582)	(606,722)
Accumulated other comprehensive loss					$ 1,520
Total other comprehensive income			(7,189)	25,171
Balances	$ (555,291)	$ (581,551)	(555,291)	$ (581,551)
Accounting Standards Update 2014-09 | Cumulative Foreign Exchange Translation Adjustments
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			(111,567)
Accounting Standards Update 2014-09 | Effective Portion of Deriviatives Designated as Hedging Instruments
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			(712)
Accumulated other comprehensive loss						$ (1,520)
Accounting Standards Update 2014-09 | Cumulative Unrecognized Actuarial Losses on Pension Obligations
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			(435,840)
Accounting Standards Update 2014-09 | Unrealized Loss on Marketable Securities
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			17
Accounting Standards Update 2014-09 | Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Income [Roll Forward]
Balances			$ (548,102)
Accumulated other comprehensive loss						$ (1,520)