DEBT - Schedule of Interest Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Convertible notes
Debt Instrument [Line Items]
Contractual interest expense	$ 4,313	$ 4,313	$ 12,939	$ 12,939
Accretion of debt discount	1,428	418	3,358	1,233
Amortization of debt issuance costs	414	642	1,670	1,897
Total	6,155	$ 5,373	17,967	$ 16,069
Line of Credit
Debt Instrument [Line Items]
Contractual interest expense	12,061		22,359
Accretion of debt discount	447		1,146
Amortization of debt issuance costs	425		1,088
Total	$ 12,933		$ 24,593

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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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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