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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	$ (4,511)	$ (4,502)	$ (13,863)	$ (14,411)
Costs of products sold (excluding depreciation and amortization) (futures contracts - copper and aluminum)	(59,461)	(75,475)	(189,604)	(250,232)
Other income (expense)	1,493	2,068	2,510	4,289
Income tax provision	(630)	(429)	1,649	(1,716)
Net income (loss) attributable to Ampco-Pittsburgh	968	(5,055)	5,778	(24,061)
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 (expense)	281	156	1,044	(287)
Income tax provision	0	0	0	0
Net income (loss) attributable to Ampco-Pittsburgh	281	156	1,044	(287)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Realized (Gains) Losses from Settlement of Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	(7)	(6)	(20)	(20)
Costs of products sold (excluding depreciation and amortization) (futures contracts - copper and aluminum)	17	59	187	196
Total before income tax	10	53	167	176
Income tax provision	0	0	0	0
Net income (loss) attributable to Ampco-Pittsburgh	$ 10	$ 53	$ 167	$ 176