ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
ACCOUNTS RECEIVABLE
Trade receivables	$ 23,257	$ 7,016
Allowance for doubtful accounts	(379)	(500)	$ (199)
Total accounts receivable	$ 22,878	$ 6,516

The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant