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Select Balance Sheet Information - Schedule of Inventories (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Finished Goods $ 20,567 $ 22,046
Work in Process 19,324 16,210
Raw Material, Fuel and Supplies 52,535 53,909
Inventories $ 92,426 $ 92,165