Convertible Senior Notes - Components of the Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jul. 23, 2018
Debt Instrument [Line Items]
Less: debt issuance costs		$ (965)
1.75% Convertible Senior Notes due 2023
Debt Instrument [Line Items]
Principal	$ 143,750
Less: debt discount, net of amortization	(26,636)
Less: debt issuance costs, net of amortization	(3,528)
Net carrying amount of the Notes	113,586
Allocated value of the conversion feature	28,916
Less: debt issuance costs	(965)
Additional paid-in capital	$ 27,951

Debt Instrument, Convertible, Carrying Amount of Equity Component, Gross

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Debt Issuance Costs, Gross, Carrying Amount of Equity Component

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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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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 (premium).

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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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