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
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	$ (5,259)	$ (5,600)
Costs of products sold (excluding depreciation andamortization) (futures contracts – copper and aluminum)	(90,221)	(87,653)
Other income	1,296	3,621
Income tax provision	(643)	463
Net (loss) income attributable to Ampco-Pittsburgh	(15,148)	941
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	161	130
Income tax provision	0	0
Net (loss) income attributable to Ampco-Pittsburgh	161	130
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)	(7)
Costs of products sold (excluding depreciation andamortization) (futures contracts – copper and aluminum)	126	(202)
Total before income tax	119	(209)
Income tax provision	0	0
Net (loss) income attributable to Ampco-Pittsburgh	$ 119	$ (209)