Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Long-term debt
Amortization of debt issuance costs			$ 308	$ 224
Convertible debt \| 3.00% Convertible senior notes due 2022
Long-term debt
Contractual interest expense	$ 1,134	$ 1,131	3,375	3,372
Amortization of debt issuance costs	86	77	249	224
Amortization of debt discount	1,725	1,546	4,999	4,487
Total	$ 2,945	$ 2,754	$ 8,623	$ 8,083
Effective interest rate of the liability component	11.00%	11.00%	11.00%	11.00%

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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