Debt - Components of Convertible Senior Notes (Details) - Convertible Senior Notes - Convertible Senior Notes - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Principal amount outstanding	$ 13,131	$ 58,503
Unamortized discount of liability component	(516)	(3,637)
Unamortized debt issuance costs	(69)	(487)
Net carrying amount of liability component	12,546	54,379
Carrying value of equity component, net of issuance costs	2,265	10,092
Carrying value of equity component, net of issuance costs	$ 25,756	$ 85,999
Fair value of outstanding Convertible Senior Notes	1 year 3 months 18 days	2 years

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fair value portion of notes payable.

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