Quarterly report pursuant to Section 13 or 15(d)

Inventories (Details)

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Inventories (Details) - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Inventory Disclosure [Abstract]    
Supplies $ 7,851 $ 9,598
Raw materials 997 746
Work in process 3,221 4,608
Finished goods 1,124 2,531
Total inventories $ 13,193 $ 17,483