Quarterly report pursuant to Section 13 or 15(d)

Inventories (Details)

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Inventories (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Inventory Disclosure [Abstract]    
Supplies $ 6,508 $ 6,312
Raw materials 637 613
Work in process 2,734 3,478
Finished goods 1,477 1,617
Total inventories $ 11,356 $ 12,020