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Environmental Matters - Summary of Environment Liability (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Environmental Exit Cost [Line Items]    
Balance at beginning of year $ 35,777 $ 32,867
Obligations settled (315) (123)
Balance at end of year 41,767 35,777
Current portion, included within accrued expenses and other current liabilities 317 188
Asset retirement obligations 41,450 35,589
Environmental Restoration Costs [Member]    
Environmental Exit Cost [Line Items]    
Balance at beginning of year 3,390 3,614
Provision for new environmental losses 210 292
Changes in estimates for previously incurred losses 1,403 354
Obligations settled (1,089) (870)
Balance at end of year 3,914 3,390
Current portion, included within accrued expenses and other current liabilities 1,710 1,520
Asset retirement obligations $ 2,204 $ 1,870