Business Segments - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable business segments | Segment				2
Impairment charge		$ 0	$ 0	$ 0	$ 10,082
Other Postretirement Benefit Plans [Member]
Segment Reporting Information [Line Items]
Curtailment gain (loss)	$ 7,639	0	7,639	0	7,654	$ 15
Akers National Roll Company [Member]
Segment Reporting Information [Line Items]
Impairment charge					10,082
Forged and Cast Engineered Products [Member]
Segment Reporting Information [Line Items]
Bad debt expenses					1,366
Forged and Cast Engineered Products [Member] | Operating Loss [Member] | Akers National Roll Company [Member]
Segment Reporting Information [Line Items]
Impairment charge					10,082
Corporate and Other [Member] | Other Expense [Member]
Segment Reporting Information [Line Items]
Dividends received		$ 1,200		$ 1,200	1,400
Corporate and Other [Member] | Other Expense [Member] | Akers National Roll Company [Member] | Other Postretirement Benefit Plans [Member]
Segment Reporting Information [Line Items]
Curtailment gain (loss)			$ 2,304		$ 2,304