Pension and Other Postretirement Benefits - Additional Information (Detail) £ in Thousands		1 Months Ended	6 Months Ended	12 Months Ended
	Jun. 01, 2018 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Pension_Plan Location Employee Customer	Dec. 31, 2018 USD ($)	Dec. 31, 2019 GBP (£) Pension_Plan	Dec. 31, 2018 GBP (£)	Dec. 31, 2017 USD ($)
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Number of employees participate in the plan | Employee				100,000
Multiemployer plan number of employees description				Approximately 100,000
Total amount of assets collected				$ 12,100,000,000
Percentage of funded status in excess				89.00%
Participation of corporation's employees in the plan				Less than 100
Participation of number of corporation's employees in the plan | Employee				100
Corporation's contributions				$ 250,000	$ 250,000
Percentage of employers contributions				5.00%
Contributions expected in 2020				$ 250,000
Service period to avail existing pension plan				10 years
Increase in projected and accumulated benefit obligations due to 1/4 percentage point decrease in discount rate				$ 8,700,000
Decrease in projected and accumulated benefit obligations due to 1/4 percentage point increase in discount rate				$ 8,700,000
Guaranteed minimum pension equalization amortization period				25 years
Maximum maturity period of fixed income investments				10 years
Investments in diversified portfolio				Invests primarily in a diversified portfolio of fixed-income securities of varying maturities or in commingled funds which invest in a diversified portfolio of fixed-income securities of varying maturities.
Target allocation				Generate a minimum annual inflation adjusted return of 5% and outperform a traditional 70/30 equities/bond portfolio.
Assumed health care cost trend rate for 2019				5.55%		5.55%
Temporary Early Retirement Incentive Program [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Special termination benefits expense					$ 1,476,000
Significant activity, description				temporary early retirement incentive program to full-time salaried participants at certain locations that either met the eligibility requirements for an unreduced pension or attained age 55 and had 3.5 years of service under the plan.
Completed years of age of full-time salaried participants					55 years
Completed years of service under the plan					3 years 6 months
Health insurance benefits, term					1 year
Maximum [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Self-sufficiency reaching period				5 years
Defined benefit plan actuarial gain loss percentage				10.00%		10.00%
Maximum [Member] | Temporary Early Retirement Incentive Program [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Unreduced pension, lump sum payment					$ 25,000
Minimum [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Self-sufficiency reaching period				3 years
Defined benefit plan actuarial gain loss percentage				10.00%		10.00%
High-quality fixed-income investments maturity				10 years
Minimum [Member] | Temporary Early Retirement Incentive Program [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Unreduced pension, lump sum payment					10,000
Multi-Employer Plan [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Number of employer locations contributed to the plan | Location				1,700
U.S. [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Curtailment gain (loss)	$ (21,000)
Decrease in liability due to remeasurement	$ 1,726,000
Percentage of employer contribution	3.00%
Percentage of matching contribution	4.00%
Defined Benefit Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember
Foreign Defined Benefits Pension Plans [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets				$ 57,900,000	49,651,000	£ 43,913	£ 38,991
Accumulated benefit obligations				54,838,000	47,459,000	£ 41,591	£ 37,269
Voluntary contributions made					982,000
Defined contribution plan contribution required in current year				0
Defined contribution plan expected contribution required in 2020 to be fully funded				0
Contributions to defined contribution pension plan				355,000	363,000
Contributions to the defined contribution pension plan expected in 2020				$ 360,000
Number of additional defined benefit pension plans | Pension_Plan				2		2
Foreign Defined Benefits Pension Plans [Member] | Unfunded Plan
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Accumulated benefit obligations				$ 7,501,000	6,878,000
Projected benefit obligations				7,501,000	6,878,000
Defined Benefit Pension Plan [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Employee benefit obligations				472,000
Defined benefit pension plan expense				$ 236,000
Special termination benefits expense		$ 3,694,000
Curtailment gain (loss)		(1,641,000)
Defined Benefit Pension Plan [Member] | U.S. [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Number of defined benefit pension plans | Pension_Plan				2		2
Minimum contributions required				$ 1,257	1,211
Minimum contributions expected in 2020				4,412,000
Fair value of plan assets				195,667,000	182,541,000			$ 199,138,000
Accumulated benefit obligations				252,808,000	226,618,000
Voluntary contributions made				1,660,000	1,614,000
Employee benefit obligations				472,000	0
Defined benefit pension plan expense				236,000	0
Special termination benefits expense				3,694,000	1,350,000
Curtailment gain (loss)				(1,641,000)	(21,000)
GMP equalization				0	0
Defined Benefit Pension Plan [Member] | Foreign Defined Benefits Pension Plans [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets				57,900,000	49,651,000			56,419,000
Voluntary contributions made				656,000	1,648,000
Employee benefit obligations				0	0
Defined benefit pension plan expense				0	0
Special termination benefits expense				0	0
Curtailment gain (loss)				0	0
GMP equalization				0	982,000
Defined Benefit Pension Plan [Member] | Ampco Pittsburgh [Member] | U.S. [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Minimum contributions expected in 2020				3,100,000
Voluntary contributions made				3,140,000	3,169,000
Nonqualified Defined Benefit Pension Plan [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Accumulated benefit obligations				8,481,000	6,852,000
Fair market value included in other noncurrent assets				4,183,000	3,659,000
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets				0	0			$ 0
Voluntary contributions made				$ 1,228,000	1,103,000
Number of subsidiaries having postretirement health care benefits | Customer				2
Employee benefit obligations				$ (4,632,000)	0
Defined benefit pension plan expense				0	0
Special termination benefits expense		478,000		(478,000)	126,000
Curtailment gain (loss)		$ 7,639,000	$ 15,000	7,654,000	0
Decrease in liability due to remeasurement				4,632,000
GMP equalization				$ 0	$ 0
Percentage decrease in other postretirement benefits in 2021				4.75%		4.75%
Year related to decrease in health care cost trend rate				2025
Other Postretirement Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items]
Monthly reimbursement period				6 years