Debt Covenant, Undrawn Availability Requirement, Amount

No definition available.

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Period Type:	instant

- Definition

Debt Covenant, Undrawn Availability Requirement, Percent Of Total Available Liquidity

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Fixed Charge Coverage Ratio

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Fixed Coverage Ratio Restriction, Minimum Borrowing Capacity

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Fixed Coverage Ratio Restriction, Percent Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Minimum Liquidity, Number of Days Prior

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No definition available.

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- Definition

Debt Instrument, Prepayment Increments, Minimum

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Increase to Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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Period Type:	instant

- 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.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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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.

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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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.

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+ Details

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- Definition

Average amount borrowed under the credit facility during the period.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Debt - Revolving Credit Facility Narrative (Details) - USD ($)	6 Months Ended
	Jun. 29, 2025	Jun. 30, 2024	Jun. 13, 2030	Jun. 13, 2026	Jun. 13, 2025	Jun. 12, 2025	Dec. 29, 2024
Debt Instrument [Line Items]
Debt issuance costs	$ 12,900,000						$ 14,200,000
Foreign credit facilities
Debt Instrument [Line Items]
Maximum borrowing capacity	72,000,000
Short-term Debt	0						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	29,400,000
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	$ 60,000,000.0
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%
Debt issuance costs					$ 2,800,000	$ 1,900,000
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
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%
2030 Term Loan
Debt Instrument [Line Items]
Outstanding borrowings	$ 200,000,000						$ 200,000,000.0
Minimum prepayment increments allowed	$ 25,000,000
2030 Term Loan \| Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Variable interest rate (percentage)	2.00%
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
Forecast \| Delayed Draw Term Loan Member
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 100,000,000