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
Long-term debt
Amortization of debt issuance costs			$ 434	$ 390
Convertible debt \| 3.00% Convertible senior notes due 2022
Long-term debt
Contractual interest expense	$ 1,134	$ 1,134	3,375	3,375
Amortization of debt issuance costs	106	95	308	277
Amortization of debt discount	2,137	1,919	6,192	5,563
Total	$ 3,377	$ 3,148	$ 9,875	$ 9,215
Effective interest rate of the liability component	11.00%	11.00%	11.00%	11.00%
Convertible debt \| 1.50% Convertible senior notes due 2026
Long-term debt
Contractual interest expense	$ 130		$ 130
Amortization of debt issuance costs	15		15
Amortization of debt discount	391		391
Total	$ 536		$ 536
Effective interest rate of the liability component	10.20%		10.20%

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

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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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