Summary of Significant Accounting Policies - Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Inventories
Raw materials and spare parts	$ 31,302	$ 28,100
Total inventory	$ 31,302	$ 28,100

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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