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Debt - Revolving Credit Facility Narrative (Details) - USD ($) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2024 | Apr. 02, 2023 | Sep. 09, 2027 | Dec. 31, 2023
Debt Instrument [Line Items] |  |  |  |
Debt issuance costs | $ 18,500,000 |  |  | $ 19,600,000
Foreign credit facilities |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Maximum borrowing capacity | 57,000,000 |  |  |
Short-term Debt | 0 |  |  | 5,000,000.0
Domestic Bank Group $600 million asset-based credit facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Bridge loan | 60,000,000 |  |  |
Amount utilized to support the issuance of letters of credit | 31,700,000 |  |  |
Average borrowings during period | 0 | $ 0 |  |
Short-term Debt | 0 |  |  | 0
Domestic Bank Group $600 million asset-based credit facility | Revolving credit facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Maximum borrowing capacity | $ 600,000,000 |  |  |
Minimum fixed charge coverage ratio allowed in event of default | 1.00 |  |  |
Percentage of borrowing capacity unavailable due to fixed charge coverage ratio covenant | 10.00% |  |  |
Borrowing capacity unavailable due to fixed charge coverage ratio covenant, minimum | $ 60,000,000 |  |  |
Minimum required liquidity number of days prior to maturity of senior notes | 90 days |  |  |
Debt covenant, undrawn availability requirement, amount | $ 120,000,000 |  |  |
Debt covenant, undrawn availability requirement, percent of total available liquidity | 20.00% |  |  |
Domestic Bank Group $600 million asset-based credit facility | Revolving credit facility | Minimum | Base rate borrowings |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Variable interest rate (percentage) | 0.25% |  |  |
Domestic Bank Group $600 million asset-based credit facility | Revolving credit facility | Minimum | Secured Overnight Financing Rate (SOFR) |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Variable interest rate (percentage) | 1.25% |  |  |
Domestic Bank Group $600 million asset-based credit facility | Revolving credit facility | Maximum | Base rate borrowings |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Variable interest rate (percentage) | 0.75% |  |  |
Domestic Bank Group $600 million asset-based credit facility | Revolving credit facility | Maximum | Secured Overnight Financing Rate (SOFR) |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Variable interest rate (percentage) | 1.75% |  |  |
Domestic Bank Group $600 million asset-based credit facility | Letter of credit sub-facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Maximum borrowing capacity | $ 200,000,000 |  |  |
2027 Term Loan |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Outstanding borrowings | 200,000,000 |  |  | 200,000,000.0
Minimum prepayment increments allowed | $ 25,000,000 |  |  |
Interest rate | 4.21% |  |  |
2027 Term Loan | Interest Rate Swap |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Notional amount of derivative | $ 50,000,000 |  |  |
2027 Term Loan | Secured Overnight Financing Rate (SOFR) |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Variable interest rate (percentage) | 2.00% |  |  |
Allegheny Ludlum 6.95% Debentures due 2025 (a) |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Outstanding borrowings | $ 150,000,000.0 |  |  | $ 150,000,000.0
Interest rate | 6.95% |  |  | 6.95%
ATI 2030 Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Outstanding borrowings | $ 425,000,000.0 |  |  | $ 425,000,000.0
Interest rate | 7.25% |  |  | 7.25%
Forecast | Domestic Bank Group $600 million asset-based credit facility | Revolving credit facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Line of credit facility, increase to maximum borrowing capacity |  |  | $ 300,000,000 |

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- Definition Short-Term financing which is expected to be paid back relatively quickly, such as by a subsequent longer-term loan. Also called swing loan or bridge financing. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(13)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)(a)(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -SubTopic 10 -Topic 210 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 + Details
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