Commitments and Contingencies (Details)		1 Months Ended	9 Months Ended
	Jun. 04, 2018 USD ($)	Aug. 31, 2005 USD ($)	Sep. 30, 2020 USD ($) case claim defendant enforcementAction	Oct. 23, 2020 USD ($)	Aug. 21, 2020 USD ($)	Apr. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 01, 2019 USD ($)	Nov. 01, 2019 BRL (R$)	Jun. 13, 2019 USD ($)	Mar. 19, 2019 USD ($)	Mar. 19, 2019 BRL (R$)
Commitments and Contingencies
Reserve for loss contingencies			$ 7,000,000.0
Penalties per day								$ 4,000	R$ 25,000		$ 900	R$ 5,000
Penalties								1,800,000	10,000,000
Current Portion of Environmental Liabilities			6,031,000				$ 3,431,000
Environmental liabilities			29,747,000				5,600,000
Total environmental liabilities			$ 35,778,000				9,031,000
Enforcement Actions | enforcementAction			3
Pennsylvania Department Of Environmental Protection, Processed Slag | Threatened Litigation
Commitments and Contingencies
Loss contingency reserves										$ 400,000
Netherlands
Commitments and Contingencies
Damages sought - interest, penalties and fees			$ 700,000
Allegheny County Health Department [Member]
Commitments and Contingencies
Penalties					$ 6,000	$ 5,000
Damages sought - interest, penalties and fees			100,000
Allegheny County Health Department [Member] | Subsequent Event
Commitments and Contingencies
Penalties				$ 8,000
Brazilian Tax Disputes - Jan 2004 through May 2005 | Sao Paulo State Revenue Authority
Commitments and Contingencies
Damages sought - interest, penalties and fees			15,000,000.0
Damages sought - principal			1,100,000
Loss contingency, reduced penalty	$ 1,100,000
Amount of damages sought	$ 6,400,000
Brazilian Tax Disputes - Jan 2002 through Dec 2003 | Sao Paulo State Revenue Authority
Commitments and Contingencies
Damages sought - interest, penalties and fees		$ 3,400,000
Damages sought - principal		1,100,000
Loss contingency, reduced penalty		800,000
Amount of damages sought		4,500,000
Loss contingency, reduced penalty, including interest		$ 9,000,000.0
Brazilian Labor Claims
Commitments and Contingencies
Loss contingency reserves			$ 4,300,000				$ 6,500,000
Other
Commitments and Contingencies
Approximate number of defendants that includes the company named in legal actions | defendant			90
Number of pending claims | claim			17,160
Number of claims dismissed to date by stipulation or summary judgment prior to trial | case			28,300
Other | Active or In Extremis docket
Commitments and Contingencies
Number of pending claims | claim			46
Other | Minimum
Commitments and Contingencies
Amount of damages sought			$ 20,000,000
Other | Maximum
Commitments and Contingencies
Amount of damages sought			$ 25,000,000
Other | New York County as managed by the New York Supreme Court
Commitments and Contingencies
Number of pending claims | case			16,596
Other | New York County as managed by the New York Supreme Court | Pending And Future Litigation, Deferred Or Inactive Docket
Commitments and Contingencies
Number of pending claims | claim			16,550
Other | New York State Supreme Court, Counties Excluding New York County
Commitments and Contingencies
Number of pending claims | case			119
Other | Courts Located In States Other Than New York
Commitments and Contingencies
Number of pending claims | case			445
CSN
Commitments and Contingencies
Penalties per day								$ 18,000	R$ 100,000		$ 4,000	R$ 20,000
Bahrain Operations, Salt Cake Processing Site [Member]
Commitments and Contingencies
Minority interest			35.00%