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, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchasecontracts)	$ (5,905)	$ (5,922)
Other income (expense)	2,900	(885)
Income tax provision	441	(135)
Net income (loss) attributable to Ampco-Pittsburgh shareholders	941	(4,783)
Costs of products sold (excluding depreciation and amortization) (futures contracts – copper and aluminum)	(94,757)	(84,781)
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)	130	733
Income tax provision	0	0
Net income (loss) attributable to Ampco-Pittsburgh shareholders	130	733
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 purchasecontracts)	(7)	(7)
Income tax provision	0	0
Net income (loss) attributable to Ampco-Pittsburgh shareholders	(209)	(155)
Costs of products sold (excluding depreciation and amortization) (futures contracts – copper and aluminum)	(202)	(148)
Total before income tax	$ (209)	$ (155)