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Accumulated Other Comprehensive Loss - Net Change and Ending Balances for Various Components of Accumulated Other Comprehensive Loss (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance $ 76,495 $ 69,459 $ 71,091 $ 71,571
Net change (632) 5,299 9,125 2,232
Ending Balance 74,559 73,676 74,559 73,676
Foreign Currency Translation [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (27,691) (23,161)
Net change     10,232 3,130
Ending Balance (17,459) (20,031) (17,459) (20,031)
Unrecognized Employee Benefit Costs [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (39,856) (40,490)
Net change     (1,343) (1,002)
Ending Balance (41,199) (41,492) (41,199) (41,492)
Cash Flow Hedges [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (102) 186
Net change     236 104
Ending Balance 134 290 134 290
Less: Noncontrolling Interest [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (813) (476)
Net change     333 146
Ending Balance (480) (330) (480) (330)
Accumulated Other Comprehensive Loss Attributable to Ampco-Pittsburgh [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (66,836) (62,989)
Net change     8,792 2,086
Ending Balance (58,044) (60,903) (58,044) (60,903)
Total Accumulated Other Comprehensive Loss [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (67,649) (63,465)
Net change     9,125 2,232
Ending Balance $ (58,524) $ (61,233) $ (58,524) $ (61,233)