Annual report pursuant to Section 13 and 15(d)

Pension And Other Postretirement Benefit Programs - Narrative (Details)

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Pension And Other Postretirement Benefit Programs - Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]    
Defined contribution plan costs $ 3,600,000 $ 5,500,000
Defined Contribution Plan, Plan A    
Defined Benefit Plan Disclosure [Line Items]    
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay 3.00%  
defined contribution plan, employer matching contribution, level 1 percent of employees' gross pay 6.00%  
Defined Contribution Plan, Plan B    
Defined Benefit Plan Disclosure [Line Items]    
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay 600.00%  
defined contribution plan, employer matching contribution, level 1 percent of employees' gross pay 4.00%  
Minimum    
Defined Benefit Plan Disclosure [Line Items]    
Defined Contribution Plan, Employer Matching Contribution, Percent of Match 50.00%  
Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Defined Contribution Plan, Employer Matching Contribution, Percent of Match 100.00%  
Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Expected employer contributions in 2019 $ 100,000  
Retiree Health and Life Insurance Plans    
Defined Benefit Plan Disclosure [Line Items]    
Other Comprehensive Income (Loss), Defined Benefit Plan, Adjustment for Settlement or Curtailment Gain (Loss), Tax $ 1,800,000  
Health care cost trend rate assumed for next fiscal year, pre-65 retiree 6.70%  
Health care cost rate assumed by 2026 4.50%  
2019 $ 4,100,000  
Expected employer contributions in 2019 4,100,000  
Liability, Defined Benefit Pension Plan 4,000,000.0 5,600,000
United States | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligation $ 418,400,000 $ 393,200,000
Expected return on plan assets (in percentage) 5.70% 6.30%
2019 $ 19,900,000  
Prepaid Expense and Other Assets, Noncurrent 1,100,000  
Liability, Defined Benefit Pension Plan   $ 11,800,000
Canadian Pension Plan | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligation $ 17,100,000 $ 16,300,000
Expected return on plan assets (in percentage) 4.00% 4.90%
2019 $ 1,300,000