Accumulated Other Comprehensive Loss - Net Change and Ending Balances for Various Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 55,616	$ 92,969
Net change	(4,397)	5,146
Ending Balance	56,179	83,734
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(18,352)	(18,642)
Net change	(4,882)	449
Ending Balance	(23,234)	(18,193)
Unrecognized Employee Benefit Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(50,859)	(30,902)
Net change	1,078	4,310
Ending Balance	(49,781)	(26,592)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	291	(64)
Net change	(593)	387
Ending Balance	(302)	323
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(68,920)	(49,608)
Ending Balance	(73,317)	(44,462)
Less Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(258)	(174)
Net change	(122)	133
Ending Balance	(380)	(41)
Accumulated Other Comprehensive Loss Attributable to Ampco-Pittsburgh [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(68,662)	(49,434)
Net change	(4,275)	5,013
Ending Balance	$ (72,937)	$ (44,421)