Notes Payable - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Interest expense recognized related to the Notes
Contractual interest expense	$ 344	$ 344
Amortization of debt issuance costs	484	458
Amortization of debt discount	5,694	5,383
Total interest expense related to the Notes	$ 6,522	$ 6,185

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 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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