Long-term Debt - Liability and Equity Component of Note (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Net carrying amount	$ 119,038	$ 55,000
Debt discount for conversion option, net of taxes	15,547
Less: Issuance costs, net of taxes	(511)
Net carrying amount	15,036
Convertible Debt \| Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Principal	143,750
Less: Unamortized debt discount	(20,716)
Unamortized debt issuance costs	(3,996)
Net carrying amount	$ 119,038

Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Net Carrying Amount

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- Definition

Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Net of Tax

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Adjustment to Additional Paid in Capital, Debt Issuance Costs Allocated to Equity, Net of Tax

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- Definition

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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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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