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Savings, Pension and Other Postretirement Employee Benefit Plans - Multiemployer Defined Benefit Plans (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost $ 5.7 $ 5.6 $ 5.7
IAM      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] No    
Multiemployer Plan, Pension, Significant, Plan Number 002    
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost $ 0.3 $ 0.3 0.3
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date May 31, 2023    
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] Red Red  
USW      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] No    
Multiemployer Plan, Pension, Significant, Plan Number 001    
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost $ 5.5 $ 5.3 $ 5.4
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date Aug. 31, 2025    
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] Red Red