Convertible Senior Notes - Summary (Details) - 2022 Notes - USD ($) $ in Thousands		3 Months Ended
Mar. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 27, 2017
Convertible Senior Notes
Principal	$ 275,000	$ 275,000	$ 275,000	$ 275,000
Less: Debt issuance costs, net	(64,568)	(64,568)	(67,630)
Net carrying amount	$ 210,432	210,432	$ 207,370
Remaining contractual life	4 years 3 months 18 days
Interest Expense
Contractual interest expense		2,034
Amortization of debt discount		3,062
Total		$ 5,096
Effective interest rate of the liability component (as a percent)	10.00%	10.00%
Level 2
Convertible Senior Notes
Fair value	$ 327,000	$ 327,000

The remaining contractual life of the convertible debt instrument.

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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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Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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Face (par) amount of debt instrument at time of issuance.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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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 issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration 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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