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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	$ (5,683)	$ (5,451)	$ (17,357)	$ (17,019)
Costs of products sold (excluding depreciation andamortization) (futures contracts – copper and aluminum)	(98,408)	(87,346)	(301,741)	(264,179)
Other income	1,671	276	5,022	(39)
Income tax provision	(800)	1,804	(907)	1,771
Net loss attributable to Ampco-Pittsburgh shareholders	(7,039)	(2,202)	(9,092)	(8,898)
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	(42)	945	152	2,461
Income tax provision	0	0	0	0
Net loss attributable to Ampco-Pittsburgh shareholders	(42)	945	152	2,461
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)	(11)	(16)	(24)
Costs of products sold (excluding depreciation andamortization) (futures contracts – copper and aluminum)	53	(139)	(239)	(448)
Total before income tax	46	(150)	(255)	(472)
Income tax provision	0	0	0	0
Net loss attributable to Ampco-Pittsburgh shareholders	$ 46	$ (150)	$ (255)	$ (472)