Long-term Debt - Interest Expense on Note (Details) - Senior notes - Convertible Senior Notes Due 2023 - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Coupon interest	$ 853	$ 853	$ 1,707	$ 1,707
Amortization of debt discount	992	937	1,969	1,860
Amortization of debt issuance costs	206	206	412	412
Total interest expense recognized	$ 2,051	$ 1,996	$ 4,088	$ 3,979

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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