Debt - Additional Information (Detail)			1 Months Ended			3 Months Ended		9 Months Ended
Debt - Additional Information (Detail)	Oct. 01, 2025 USD ($)	Sep. 29, 2022 USD ($)	Oct. 31, 2025 USD ($)	Jun. 30, 2023 USD ($)	Aug. 31, 2022 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024	Sep. 30, 2025 USD ($) Bond	Sep. 30, 2024	Oct. 10, 2025 USD ($)	Oct. 09, 2025 USD ($)	Jun. 25, 2025 USD ($)	Dec. 31, 2024 USD ($)	Oct. 14, 2022
Line Of Credit Facility [Line Items]
Swing loans						$ 2,030,000		$ 2,030,000					$ 0
Life of underlying asset								15 years
Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity												$ 125,000,000
Maturity date								Jun. 25, 2030
Credit agreement modification								As modified, the Trigger Period will commence on any day in which the Undrawn Availability is less than the greater of 12.50% (previously 15%) of the Maximum Revolving Advance Amount or $12,500 (previously $15,000) and will terminate on any day in which the Undrawn Availability is more than the greater of 12.50% (previously 15%) of the Maximum Revolving Advance Amount or $12,500 (previously $15,000) for 30 consecutive days (collectively, the “Trigger Period Modification Consent”). Immediately upon expiration of the 45 consecutive day period, the definition of the Trigger Period will revert to the definition in effect immediately prior to the Trigger Period Modification Consent.
Long term debt						50,530,000		$ 50,530,000					56,000,000
Line of credit, remaining borrowing capacity						28,189,000		28,189,000
Debt issuance costs						$ 891,000		$ 891,000
Effective interest rate during period						7.38%	8.26%	7.22%	8.24%
Revolving Credit Facility [Member] \| Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Maximum revolving advance amount percentage of undrawn availability of credit agreement										12.50%	15.00%
Line of credit, remaining borrowing capacity										$ 12,500,000	$ 15,000,000
Trigger period for structured insolvency										45 days
Trigger period under the credit agreement for structured insolvency										45 days
Revolving Credit Facility [Member] \| Minimum [Member]
Line Of Credit Facility [Line Items]
Fixed charge coverage ratio						1.05		1.05
Revolving Credit Facility [Member] \| SOFR [Member]
Line Of Credit Facility [Line Items]
Debt instrument description of interest rate								Secured Overnight Financing Rate (“SOFR”) plus an applicable margin ranging between 2.00% and 2.50%.
Revolving Credit Facility [Member] \| SOFR [Member] \| Minimum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread								2.00%
Revolving Credit Facility [Member] \| SOFR [Member] \| Maximum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread								2.50%
Revolving Credit Facility [Member] \| Senior Secured Asset-Based Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity												100,000,000
Revolving Credit Facility [Member] \| Letter of Credit [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity												40,000,000
Revolving Credit Facility [Member] \| European Credit Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity												30,000,000
Sale and Leaseback Financing Obligations [Member]
Line Of Credit Facility [Line Items]
Long term debt						$ 46,115,000		$ 46,115,000					45,451,000
Lessee lease term														20 years
Lessee, operating lease, option to extend								however, UES may extend the lease for the Properties for four successive periods of five years each. If fully extended, the Restated Lease would expire in August 2062
Lessee, operating term period														5 years
Extended lease expiration date														2062-08
Lease repurchase percentage on lessor investment for properties														115.00%
Effective interest rate during period						8.29%	8.25%	8.28%	8.24%
Rental properties						$ 3,719,000		$ 3,719,000
Sale and Leaseback Financing Obligations [Member] \| Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Incremental percentage on annual lease payment	2.04%
Rental properties	$ 3,795,000
Sale and Leaseback Financing Obligations [Member] \| Capital Additions [Member]
Line Of Credit Facility [Line Items]
Estimated cost on upgrading existing equipment					$ 2,500,000
Proceeds from disbursement agreement				$ 2,500,000
Annual rent adjustment to repay restated lease					$ 2,500,000
Sale and Leaseback Financing Obligations [Member] \| Maximum [Member]
Line Of Credit Facility [Line Items]
Incremental percentage on annual lease payment								2.04%
Change in consumer price index ratio								1.25
Equipment Financing Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity		$ 20,000,000
Long term debt						$ 15,187,000		$ 15,187,000					16,782,000
Payments of principal and interest								$ 293,000
Debt instrument, maturity date, description								2031
Debt Instrument, Term		84 months
Equipment Financing Facility [Member] \| Term Notes [Member]
Line Of Credit Facility [Line Items]
Effective interest rate during period						8.66%	8.69%	8.66%	8.60%
Equipment Financing Facility [Member] \| Term Notes [Member] \| Minimum [Member]
Line Of Credit Facility [Line Items]
Percentage of converted fixed interest rate								8.40%
Equipment Financing Facility [Member] \| Term Notes [Member] \| Maximum [Member]
Line Of Credit Facility [Line Items]
Percentage of converted fixed interest rate								9.22%
Equipment Term Notes [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity						$ 13,500,000		$ 13,500,000				13,500,000
Frequency of payment and payment terms, description								On June 25, 2025, the Corporation borrowed $13,500 with such proceeds used to paydown borrowings under the Revolving Credit Facility. The Equipment Term Notes are payable in equal monthly installments of principal of $161 commencing August 1, 2025, and continuing on the first day of each month through June 2030, followed by the sixtieth payment of all unpaid principal, accrued and unpaid interest and all unpaid fees, unless otherwise refinanced.
Borrowed amount												$ 13,500,000
Monthly installment								$ 161,000
Principal payments term,Description								principal payments due under the Equipment Term Notes during the next 12 months
Long term debt						$ 13,179,000		$ 13,179,000
Effective interest rate during period						7.94%
Equipment Term Notes [Member] \| Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Repayment of borrowings			$ 2,798,000
Equipment Term Notes [Member] \| SOFR [Member]
Line Of Credit Facility [Line Items]
Debt instrument description of interest rate								Borrowings under the Equipment Term Notes will bear interest at SOFR plus an applicable margin ranging between 3.00% and 3.50%.
Equipment Term Notes [Member] \| SOFR [Member] \| Minimum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread								3.00%
Equipment Term Notes [Member] \| SOFR [Member] \| Maximum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread								3.50%
Industrial Revenue Bonds ("IRB") [Member]
Line Of Credit Facility [Line Items]
Long term debt						$ 9,191,000		$ 9,191,000					$ 9,191,000
Number of industrial revenue bonds \| Bond								2
Industrial Revenue Bonds ("IRB") [Member] \| Taxable Industrial Revenue Bond [Member]
Line Of Credit Facility [Line Items]
Long term debt						$ 7,116,000		$ 7,116,000
Interest at a floating rate on IRB maturing in 2027/2029						4.41%	0.40%	4.42%	5.40%
Industrial Revenue Bonds ("IRB") [Member] \| Tax Exempt Industrial Revenue Bond Two [Member]
Line Of Credit Facility [Line Items]
Long term debt						$ 2,075,000		$ 2,075,000
Interest at a floating rate on IRB maturing in 2027/2029						2.82%	3.62%	3.08%	3.80%

AMPCO PITTSBURGH CORP 10-Q