Pension and Other Postretirement Benefits - Additional Information (Detail) £ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Customer Pension_Plan Employees Location	Dec. 31, 2016 GBP (£) Customer Employees Location	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 GBP (£) Pension_Plan	Dec. 31, 2015 GBP (£)
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined benefit pension contribution plan, non-elective base contribution rate	3.00%	3.00%
Number of employees participate in the plan | Employees	100,000	100,000
Multiemployer plan number of employees description	Approximately 100,000	Approximately 100,000
Total amount of assets collected	$ 11,600,000,000
Percentage of funded status in excess	101.00%	101.00%
Participation of corporation's employees in the plan	Less than 100	Less than 100
Corporation's contributions	$ 237,000		$ 236,000	$ 233,000
Percentage of employers contributions	5.00%				5.00%
Contributions expected in 2017	$ 259,000
Contributions to defined contribution pension plan | £		£ 1,123
Service period to avail existing pension plan	15 years	15 years
Maximum maturity period of fixed income investments	10 years	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.	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.	Generate a minimum annual inflation adjusted return of 5% and outperform a traditional 70/30 equities/bond portfolio.
High-quality fixed-income investments maturity	10 years	10 years
Assumed health care cost trend rate for 2017	6.00%	6.00%
Akers AB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Employer non-elective contributions, percentage of employee compensation	3.00%	3.00%
Reduction in pension liability due to exit from defined benefit plan	$ 1,181,000
Curtailment gain (loss)	$ 887,000
Number of postretirement benefit plans | Pension_Plan	2				2
Ampco Pittsburgh [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Voluntary contributions made	$ 2,466,000		882,000
Employer contribution expected in 2017	$ 2,810,000
Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined benefit plan actuarial gain loss percentage	10.00%				10.00%
Minimum [Member] | Multi-Employer Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Number of employer locations contributed to the plan | Location	1,650	1,650
Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined benefit pension contribution plan, matching contribution rate	4.00%	4.00%
Defined benefit plan actuarial gain loss percentage	10.00%				10.00%
U.S. Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Number of defined benefit pension plans | Pension_Plan	1				1
Curtailment gain (loss)	$ 887,000		(1,303,000)	0
Voluntary contributions made	376,000		324,000
Minimum contributions required	0
Estimated benefit payments, in 2017	13,206,000
Estimated benefit payments, in 2018	13,535,000
Estimated benefit payments, in 2019	13,944,000
Estimated benefit payments, in 2020	14,195,000
Estimated benefit payments, in 2021	14,485,000
Estimated benefit payments, in 2022-2026	73,814,000
Fair value of plan assets	188,722,000		139,376,000	157,048,000
Accumulated benefit obligations	235,299,000		173,243,000
Projected benefit obligations	68,081,000		0
Reduction in plan liability	$ 0		447,000
U.S. Pension Benefits [Member] | Akers AB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Number of defined benefit pension plans | Pension_Plan	2				2
Nonqualified Defined Benefit Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Minimum contributions expected in 2017	$ 0
Estimated benefit payments, in 2017	417,000
Estimated benefit payments, in 2018	438,000
Estimated benefit payments, in 2019	452,000
Estimated benefit payments, in 2020	463,000
Estimated benefit payments, in 2021	482,000
Estimated benefit payments, in 2022-2026	2,548,000
Accumulated benefit obligations	6,639,000		5,676,000
Defined benefit plan contribution made to trusts	0
Fair market value included in other noncurrent assets	3,863,000		3,663,000
Foreign Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Curtailment gain (loss)	0		0	0
Voluntary contributions made	1,687,000		1,715,000	1,849,000
Estimated benefit payments, in 2017	1,249,000
Estimated benefit payments, in 2018	1,752,000
Estimated benefit payments, in 2019	2,042,000
Estimated benefit payments, in 2020	1,906,000
Estimated benefit payments, in 2021	1,883,000
Estimated benefit payments, in 2022-2026	11,679,000
Fair value of plan assets	48,055,000		49,628,000	50,533,000	£ 38,955	£ 33,528
Accumulated benefit obligations	61,277,000		63,750,000		£ 49,673	£ 43,069
Contributions to defined contribution pension plan	252,000		382,000	407,000
Contributions to the defined contribution pension plan expected in 2017	276,000
Projected benefit obligations	5,393,000		0
Reduction in plan liability	$ 0		0
Foreign Pension Benefits [Member] | Akers AB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Number of defined benefit pension plans | Pension_Plan	2				2
Estimated benefit payments, in 2017	$ 189,000
Estimated benefit payments, in 2018	224,000
Estimated benefit payments, in 2019	274,000
Estimated benefit payments, in 2020	274,000
Estimated benefit payments, in 2021	306,000
Estimated benefit payments, in 2022-2026	1,333,000
Projected benefit obligations	5,633,000
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Curtailment gain (loss)	0		0	0
Voluntary contributions made	1,391,000		610,000
Estimated benefit payments, in 2017	1,289,000
Estimated benefit payments, in 2018	1,331,000
Estimated benefit payments, in 2019	1,358,000
Estimated benefit payments, in 2020	1,455,000
Estimated benefit payments, in 2021	1,279,000
Estimated benefit payments, in 2022-2026	5,825,000
Fair value of plan assets	0		0	$ 0
Projected benefit obligations	$ 17,467,000		$ 0
Number of subsidiary having postretirement health care benefits | Customer	1	1
Monthly reimbursement period			5 years
Reduction in plan liability	$ (4,762,000)		$ (4,437,000)
Percentage decrease in other postretirement benefits in 2018	4.75%	4.75%
Year related to decrease in health care cost trend rate	2020				2020
Percentage point increase or decrease in the assumed health care cost trend rate	1.00%	1.00%
Other Postretirement Benefits [Member] | Akers AB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Reduction in pension liability due to exit from defined benefit plan	$ 4,762,000
Other Postretirement Benefits [Member] | Minimum [Member] | Akers AB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Amortization period of pension liability	7 years 6 months	7 years 6 months
Other Postretirement Benefits [Member] | Maximum [Member] | Akers AB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Amortization period of pension liability	12 years	12 years
Remeasurement of Pension Plan Liability [Member] | Electric Steel Corporation Carnegie [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Curtailment gain (loss)			(1,303,000)
Pension benefit plan decrease in liability			$ 10,306,000