Accumulated Other Comprehensive Loss - Net Change and Ending Balances for Various Components of Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 92,969	$ 161,761
Net Change	(19,312)	(4,219)
Ending Balance	55,616	92,969
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(18,642)	(11,932)
Net Change	290	(6,710)
Ending Balance	(18,352)	(18,642)
Unrecognized Components of Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(30,902)	(34,196)
Net Change	(19,957)	3,294
Ending Balance	(50,859)	(30,902)
Realized Losses (Gains) from Settlement of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(64)	739
Net Change	355	(803)
Ending Balance	291	(64)
Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(174)	3
Net Change	(84)	(177)
Ending Balance	(258)	(174)
Accumulated Other Comprehensive Loss Attributable to Ampco-Pittsburgh [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(49,434)	(45,392)
Net Change	(19,228)	(4,042)
Ending Balance	(68,662)	(49,434)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(49,608)	(45,389)
Ending Balance	$ (68,920)	$ (49,608)