Convertible Senior Notes Due 2023 - Summary of 2023 Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Mar. 15, 2018
Debt Instrument [Line Items]
Carrying value of the convertible notes	$ 345,170	$ 329,462
2023 Notes
Debt Instrument [Line Items]
Principal amount of the 2023 Notes	402,500	402,500	$ 402,500
Unamortized debt discount and deferred financing costs	(57,330)	(73,038)
Carrying value of the convertible notes	$ 345,170	$ 329,462

Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Convertible Notes Payable, excluding current portion. Convertible Notes Payable is a written promise to pay a note which can be exchanged for a specified amount of another, related security, at the option of the issuer and the holder.

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