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Employee Benefits - Additional Information (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) Productionfacility | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Mar. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Payment for Other Postretirement Benefits |  | $ 2,900,000 | $ 2,100,000 | $ 15,700,000 |
Accrued annual contribution to VEBAs |  | 1,700,000 | 2,900,000 |  |
Union VEBA |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Accrued annual contribution to VEBAs |  |  |  |  | $ 12,800,000
Postretirement Health Coverage | Salaried VEBA |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Maximum contribution threshold |  | 2,900,000 |  |  |
Payment for Other Postretirement Benefits | $ 2,900,000 |  |  |  |
Canadian pension plan | Canadian pension plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, accumulated benefit obligation |  | 9,200,000 | $ 7,600,000 |  |
Defined benefit plan, expected future employer contributions, next fiscal year |  | $ 300,000 |  |  |
Canadian pension plan | Canadian pension plan | Equity Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, plan assets, actual allocation, percentage |  | 58.00% |  |  |
Defined benefit plan, plan assets, target allocation, percentage |  | 60.00% |  |  |
Canadian pension plan | Canadian pension plan | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, plan assets, actual allocation, percentage |  | 35.00% |  |  |
Defined benefit plan, plan assets, target allocation, percentage |  | 35.00% |  |  |
Canadian pension plan | Canadian pension plan | Short-term Investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, plan assets, actual allocation, percentage |  | 7.00% |  |  |
Defined benefit plan, plan assets, target allocation, percentage |  | 5.00% |  |  |
Hourly bargaining unit employees |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Number of production facilities | Productionfacility |  | 9 |  |  |
Hourly bargaining unit employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Number of production facilities | Productionfacility |  | 3 |  |  |
Hourly bargaining unit employees | Concurrent match |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Number of production facilities | Productionfacility |  | 1 |  |  |
Hourly bargaining unit employees | Fixed rate and concurrent match |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Number of production facilities | Productionfacility |  | 3 |  |  |
Hourly bargaining unit employees | No contributions required |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Number of production facilities | Productionfacility |  | 2 |  |  |
Salaried and certain hourly employee | Concurrent match |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan employer concurrent match percentage |  | 4.00% |  |  |
Hired on or after January 1, 2004 | Hourly bargaining unit employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan annual employer contribution percentage |  | 2.00% |  |  |
Hired on or after January 1, 2004 | Certain salaried and hourly employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan annual employer contribution percentage |  | 2.00% |  |  |
Minimum |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated annual contribution to pension and other postretirement benefit plans |  | $ 3,000,000.0 |  |  |
Minimum | Hourly bargaining unit employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan, employer discretionary contribution amount |  | $ 800 |  |  |
Minimum | Hired prior to January 1, 2004 | Hourly bargaining unit employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan annual employer contribution percentage |  | 2.00% |  |  |
Minimum | Hired prior to January 1, 2004 | Salaried and certain hourly employee | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan annual employer contribution percentage |  | 2.00% |  |  |
Maximum |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated annual contribution to pension and other postretirement benefit plans |  | $ 5,000,000.0 |  |  |
Maximum | Salaried VEBA |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated annual contribution to pension and other postretirement benefit plans |  | 1,700,000 |  |  |
Maximum | Hourly bargaining unit employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan, employer discretionary contribution amount |  | $ 2,400 |  |  |
Maximum | Hired prior to January 1, 2004 | Hourly bargaining unit employees | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan annual employer contribution percentage |  | 10.00% |  |  |
Maximum | Hired prior to January 1, 2004 | Salaried and certain hourly employee | Fixed rate contributions |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan annual employer contribution percentage |  | 10.00% |  |  |

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