Accumulated Other Comprehensive Loss - Line Items Affected on Consolidated Statements of Operations for Components Reclassified from Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	$ (18,967)	$ (21,379)
Costs of products sold (excluding depreciation and amortization) (futures contracts – copper and aluminum)	(326,157)	(351,839)
Other expense	6,466	4,682
Income tax provision	(2,108)	(268)
Net loss attributable to Ampco-Pittsburgh	(20,986)	(69,335)
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 expense	(302)	89
Income tax provision	0	0
Net loss attributable to Ampco-Pittsburgh	(302)	89
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Realized Losses (Gains) from Settlement of Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	(27)	(23)
Costs of products sold (excluding depreciation and amortization) (futures contracts – copper and aluminum)	285	(67)
Total before income tax	258	(90)
Income tax provision	0	0
Net loss attributable to Ampco-Pittsburgh	$ 258	$ (90)