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Employee Benefits - Additional Information (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items] |  |  |
Payment for Other Postretirement Benefits | $ 1,700,000 | $ 2,900,000 |
Warrick Rolling Mill | Other Accrued Liabilities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Accumulated benefit obligation | 1,000,000.0 |  |
Postretirement Health Coverage | Salaried VEBA |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Maximum contribution threshold |  |  | $ 2,900,000
Payment for Other Postretirement Benefits | 1,700,000 |  |
Pension Plan | Warrick Rolling Mill |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Accumulated benefit obligation | 6,700,000 |  |
Expected minimum employer contributions in 2021 | 100,000 |  |
Other Postretirement Benefits Plan | Warrick Rolling Mill |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Accumulated benefit obligation | 78,000,000.0 |  |
Expected minimum employer contributions in 2021 | 700,000 |  |
Level 2 | Fair Value, Measurements, Recurring |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of deferred compensation assets | 9,500,000 |  | $ 9,600,000
Accrued salaries, wages and related expenses |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Accrued salaries, wages and related expenses | $ 2,700,000 |  |

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- Definition Carrying value as of the balance sheet date of obligations incurred and payable for incentive compensation awarded to employees and directors or earned by them based on the terms of one or more relevant arrangements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15(a)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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