Accumulated Other Comprehensive Loss - Line Items Affected on Condensed Consolidated Statements of Operations for Components Reclassified from Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	$ (4,279)	$ (4,511)	$ (13,515)	$ (13,863)
Costs of products sold (excluding depreciation and amortization) (futures contracts - copper and aluminum)	(67,990)	(59,461)	(213,011)	(189,604)
Other income – net	2,006	1,493	4,694	2,510
Income tax (provision) benefit	(291)	(630)	(2,044)	1,649
Net (loss) income attributable to Ampco-Pittsburgh	(1,589)	968	(359)	5,778
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Amortization of Unrecognized Employee Benefit Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income – net	472	281	1,418	1,044
Income tax (provision) benefit	(15)	0	(47)	0
Net (loss) income attributable to Ampco-Pittsburgh	457	281	1,371	1,044
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Settlements of Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	(6)	(7)	(20)	(20)
Costs of products sold (excluding depreciation and amortization) (futures contracts - copper and aluminum)	(298)	17	(1,004)	187
Total before income tax	(304)	10	(1,024)	167
Income tax (provision) benefit	0	0	0	0
Net (loss) income attributable to Ampco-Pittsburgh	$ (304)	$ 10	$ (1,024)	$ 167