Commitments and Contingencies (Details)			1 Months Ended	6 Months Ended
	Apr. 01, 2020 USD ($) enforcementAction	Jun. 04, 2018 USD ($)	Aug. 31, 2005 USD ($)	Jun. 30, 2020 USD ($) case defendant claim enforcementAction	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						$ 5,000	R$ 25,000		$ 900	R$ 5,000
Penalties						1,900,000	10,000,000
Current Portion of Environmental Liabilities				6,115,000	$ 3,431,000
Total Environmental Liabilities				$ 36,142,000	9,031,000
Enforcement Actions | enforcementAction				3
Events | 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				$ 500,000
Allegheny County Health Department [Member]
Commitments and Contingencies
Penalties	$ 4,500
Damages sought - interest, penalties and fees				100,000
Brazilian Tax Disputes - Jan 2004 through May 2005 | Sao Paulo State Revenue Authority
Commitments and Contingencies
Damages sought - interest, penalties and fees				15,700,000
Damages sought - principal				1,100,000
Loss contingency, reduced penalty		$ 1,000,000
Amount of damages sought		$ 7,000,000
Brazilian Tax Disputes - Jan 2002 through Dec 2003 | Sao Paulo State Revenue Authority
Commitments and Contingencies
Damages sought - interest, penalties and fees			$ 3,600,000
Damages sought - principal			1,100,000
Loss contingency, reduced penalty			1,100,000
Amount of damages sought			4,700,000
Loss contingency, reduced penalty, including interest			$ 9,300,000
Brazilian Labor Claims
Commitments and Contingencies
Loss contingency reserves				$ 4,600,000	$ 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				17,140
Number of claims dismissed to date by stipulation or summary judgment prior to trial | case				28,253
Other | Active or In Extremis docket
Commitments and Contingencies
Number of pending claims | claim				35
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				16,585
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				117
Other | Courts Located In States Other Than New York
Commitments and Contingencies
Number of pending claims | case				438
CSN
Commitments and Contingencies
Penalties per day						$ 19,000	R$ 100,000		$ 4,000	R$ 20,000
Bahrain Operations, Salt Cake Processing Site [Member]
Commitments and Contingencies
Minority interest				35.00%