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Inventory (Tables)
6 Months Ended
Jun. 30, 2020
Inventory Disclosure [Abstract]  
Schedule of inventories

Inventory as of December 31, 2019 and June 30, 2020 consisted of the following (in thousands):

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December 31, 

    

June 30, 

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2019

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2020

Raw materials and spare parts

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$

29,874

​

$

29,503

Total inventory

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$

29,874

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$

29,503