Employee Benefits - Expected Benefit Payments (Details) $ in Millions	Mar. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
2021	$ 0.8
2022	1.7
2023	2.5
2024	3.3
2025	4.2
2026-2030	31.6
Pension Plan \| Warrick Rolling Mill
Defined Benefit Plan Disclosure [Line Items]
2021	0.1
2022	0.1
2023	0.2
2024	0.3
2025	0.5
2026-2030	4.4
Other Postretirement Benefits Plan \| Warrick Rolling Mill
Defined Benefit Plan Disclosure [Line Items]
2021	0.7
2022	1.6
2023	2.3
2024	3.0
2025	3.7
2026-2030	$ 27.2

Defined benefit plan, expected future benefit payment, after year four for next five years.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Amount of benefit for defined benefit plan expected to be paid in remainder of current fiscal year.

+ References

No definition available.

+ Details

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- Definition

Amount of benefit for defined benefit plan expected to be paid in fourth fiscal year following current fiscal year.

+ References

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- Definition

Amount of benefit for defined benefit plan expected to be paid in third fiscal year following current fiscal year.

+ References

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- Definition

Amount of benefit for defined benefit plan expected to be paid in second fiscal year following current fiscal year.

+ References

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