DEBT - Schedule of Convertible Senior Notes due 2023 (Details) - Convertible Notes - Convertible Senior Notes Due 2023 - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Contractual interest expense	$ 50	$ 50	$ 150	$ 150
Amortization of debt issuance costs	10	10	30	30
Total interest cost recognized	$ 60	$ 60	$ 180	$ 180

Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Name:	us-gaap_InterestExpenseDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration