Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Schedule of Restrictions on Cash and Cash Equivalents) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 14,472	$ 15,645	$ 17,976	$ 11,641
Restricted cash in restricted deposits	445		418
Total cash, cash equivalents, and restricted cash shown in the consolidated statements of cash flows	$ 14,917	16,092	$ 18,394	12,197	$ 3,610
Prepaid Expenses and Other Current Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash in restricted deposits		0		140
Restricted Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash in restricted deposits		$ 447		$ 416