INDEBTEDNESS - Convertible Senior Notes, Term Loan, and Delayed Draw Term Loan (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
INDEBTEDNESS
Contractual coupon	$ 6,635	$ 7,170	$ 4,313
Amortization of debt discount	5,647	7,002	6,720
Amortization of finance fees	1,377	1,463	845
Capitalized interest	(191)	(724)	(554)
Interest Expense, Debt	$ 13,468	$ 14,911	$ 11,324

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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Amount of interest costs capitalized disclosed as an adjusting item to interest costs incurred.

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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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