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, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Depreciation and amortization (foreign currency purchase contracts)	$ (4,699)	$ (5,259)
Costs of products sold (excluding depreciation and amortization) (futures contracts - copper and aluminum)	(70,160)	(90,221)
Other income	(1,320)	1,296
Income tax provision	2,783	(643)
Net income (loss) attributable to Ampco-Pittsburgh	4,142	(15,148)
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	385	161
Income tax provision	0	0
Net income (loss) attributable to Ampco-Pittsburgh	385	161
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 and amortization) (futures contracts - copper and aluminum)	(8)	126
Total before income tax	(15)	119
Income tax provision	0	0
Net income (loss) attributable to Ampco-Pittsburgh	$ (15)	$ 119