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%