The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

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-Name Regulation 12B
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Estimated annual contribution to pension and other postretirement benefit plans.

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Monthly contributions per hour worked by each bargaining unit employee.

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Multiemployer Pension Plan Disclosure [Line Items]

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Multiemployer Plans, Collective Bargaining Arrangement, Percentage Of Employer's Participants To All Employees

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Number of collective-bargaining agreements

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Percentage of contributions required by collective bargaining arrangement to all contributions required of employer for pension and other postretirement plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
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Amount of contributions made to multiemployer plan by employer.

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Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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-SubTopic 80
-Section 50
-Paragraph 5
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Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire first in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire last in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Percentage of employee participants subject to a collective bargaining arrangement to all of the employer's participants in a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Indicate whether a funding improvement plan or rehabilitation plan has been implemented or is pending for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "pending", "implemented", "other", and "NA".

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-SubTopic 80
-Section 50
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Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA".

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Multiemployer Pension Plans (Details)	12 Months Ended
Multiemployer Pension Plans (Details)	Dec. 31, 2018 USD ($) agreements	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Multiemployer Pension Plan Disclosure
Percentage of employees participating in multiemployer pension plans to total employees	51.00%
Contributions of the Company	$ 4,700,000	$ 4,600,000	$ 4,700,000
Company's contributions to the multiemployer plans is less than	5.00%
USW Plan
Multiemployer Pension Plan Disclosure
Employer Identification Number	236648508
Pension Protection Act Zone Status	Green	Green
FIP/RP Status Pending/Implemented in Current Year	No
Contributions of the Company	$ 3,600,000	$ 3,500,000	3,700,000
Surcharge Imposed in 2018	No
Expiration Date of Collective-Bargaining Agreement, First	Mar. 31, 2020
Expiration Date of Collective-Bargaining Agreement, Last	Feb. 28, 2021
Number of collective-bargaining agreements \| agreements	3
USW Plan \| Newark, Ohio and Spokane (Trentwood), Washington Facilities
Multiemployer Pension Plan Disclosure
Percentage of employees covered by bargaining agreement	86.00%
USW Plan \| Newark, Ohio and Spokane (Trentwood), Washington Facilities \| Starting July 2015
Multiemployer Pension Plan Disclosure
Monthly contributions per hour worked by each bargaining unit employee	$ 1.50
USW Plan \| Newark, Ohio and Spokane (Trentwood), Washington Facilities \| Ending in July Two Thousand Nineteen
Multiemployer Pension Plan Disclosure
Monthly contributions per hour worked by each bargaining unit employee	$ 1.75
USW Plan \| Richmond (Bellwood), Virginia Facility
Multiemployer Pension Plan Disclosure
Percentage of employees covered by bargaining agreement	11.00%
USW Plan \| Florence, Alabama Facility
Multiemployer Pension Plan Disclosure
Percentage of employees covered by bargaining agreement	3.00%
Other Funds
Multiemployer Pension Plan Disclosure
Contributions of the Company	$ 1,100,000	$ 1,100,000	$ 1,000,000.0
Multiemployer Plans, Pension \| Minimum
Multiemployer Pension Plan Disclosure
Estimated annual contribution to pension and other postretirement benefit plans	3,000,000.0
Multiemployer Plans, Pension \| Maximum
Multiemployer Pension Plan Disclosure
Estimated annual contribution to pension and other postretirement benefit plans	$ 5,000,000.0