Convertible Notes Payable - Summary of Total Interest Expense Recognized Related to the Convertible Notes (Details) - Convertible debt - 3.00% Convertible notes - 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]
Contractual interest expense	$ 2,288	$ 2,288	$ 4,575	$ 4,575
Amortization of debt discount	4,275	3,737	8,409	7,351
Amortization of debt issuance costs	160	140	315	276
Total interest expense	$ 6,723	$ 6,165	$ 13,299	$ 12,202

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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