Notes Payable - 2.25% Convertible Senior Notes Due 2022 - Total Interest Expense (Details) - 2.25% Convertible Senior Notes due 2022 - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Interest Expense
Contractual interest expense	$ 1,805	$ 1,888
Amortization of debt issuance costs	346	272
Amortization of debt discount	5,069	4,075
Total interest expense	$ 7,220	$ 6,235

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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