Debt Debt schedule (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 08, 2014
Debt Instrument [Line Items]
Less: current portion	$ 10,184	$ 0
Long-term debt	227,394	0
Convertible Debt [Member] \| 3.25% Convertible Senior Notes due 2020 [Member]
Debt Instrument [Line Items]
Principal amount of Convertible Senior Notes outstanding	167,314	167,314
Unamortized deferred issuance costs	(15,356)	(20,221)
Unamortized deferred issuance costs		(4,200)
Net carrying amount of liability component	149,868	144,340
Less: current portion	0	0
Long-term debt	149,868	144,340
Carrying value of equity component, net of issuance costs	29,211	29,211	$ 30,700
Fair value of outstanding Convertible Senior Notes	$ 257,245	$ 165,223
Remaining amortization period of discount on the liability component	3 years	4 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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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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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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. 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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