LONG-TERM DEBT, LETTERS OF CREDIT AND DERIVATIVES - Components of Convertible Debt Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Amortization of debt discount and issuance costs			$ 5,691	$ 5,208
Interest expense, net	$ 7,647	$ 8,022	22,658	23,250
Convertible debt
Debt Instrument [Line Items]
Coupon interest	2,875	2,875	8,625	8,625
Amortization of debt discount and issuance costs	1,633	1,493	4,778	4,371
Interest expense, net	$ 4,508	$ 4,368	$ 13,403	$ 12,996
Effective interest rate	9.12%	9.12%	9.12%	9.12%

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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-Topic 230
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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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-Publisher FASB
-Name Accounting Standards Codification
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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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