DEBT - Schedule of Convertible Senior Notes due 2023 (Details) - Convertible Notes - Convertible Senior Notes Due 2023 - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Contractual interest expense	$ 1,226	$ 975
Amortization of debt issuance costs	245	193
Total interest cost recognized	$ 1,471	$ 1,168

Amount of amortization expense attributable to debt issuance costs.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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

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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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