Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Term Loan \| Secured Debt
Debt Instrument [Line Items]
Contractual interest expense	$ 0	$ 0	$ 0	$ 1,667
Amortization of debt discount	0	0	0	859
Amortization of debt issuance costs	0	0	0	103
Total interest expense	0	0	0	2,629
2025 Notes \| Convertible Debt
Debt Instrument [Line Items]
Contractual interest expense	1,315	1,278	3,899	2,078
Amortization of debt discount	207	217	622	341
Amortization of debt issuance costs	165	172	495	268
Total interest expense	1,687	1,667	5,016	2,687
2022 Notes \| Convertible Debt
Debt Instrument [Line Items]
Contractual interest expense	0	0	0	768
Amortization of debt discount	0	0	0	1,952
Amortization of debt issuance costs	0	0	0	111
Total interest expense	$ 0	$ 0	$ 0	$ 2,831

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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