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Inventory - Schedule of Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Allowance for obsolescence	$ 37	$ 221	$ 24
Raw materials - current	20,381	18,026
Work-in-process	1,011	1,900
Inventory - current	21,392	19,926
Raw materials - long term (net of allowances of $37 and $221, respectively)	1,250	1,065
Inventory - total	$ 22,642	$ 20,991

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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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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of unprocessed items to be consumed in the manufacturing or production process.

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