Convertible Senior Notes Due 2023 - Summary of liability component of 2023 Notes (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total carrying value	$ 341,163	$ 329,462
2023 Notes
Debt Instrument [Line Items]
Principal amount of the 2023 Notes	402,500	402,500
Debt discount	(76,434)	(76,434)
Deferred financing costs	(8,452)	(8,452)
Accretion of debt discount and deferred financing costs	23,549	11,848
Total carrying value	$ 341,163	$ 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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Face (par) amount of debt instrument at time of issuance.

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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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No definition available.

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- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

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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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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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