Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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 of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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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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Convertible Notes - Components and Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Convertible Notes
Convertible senior notes	$ 16,608	$ 651,481
Total debt	26,800
Annual maturities of Convertible Notes
2018	7,700
2020	19,100
Total debt	26,800
Carrying Amount
Convertible Notes
Convertible senior notes	24,001	651,481
Total debt	24,001	651,481
Less current portion	7,393
Long-term debt, noncurrent	16,608	651,481
Annual maturities of Convertible Notes
Total debt	$ 24,001	$ 651,481
Convertible Senior Notes 0.375 Percent Due 2018
Convertible Notes
Interest rate of debt (as a percent)	0.375%	0.375%
Convertible Senior Notes 0.375 Percent Due 2018 \| Carrying Amount
Convertible Notes
Convertible senior notes	$ 7,393	$ 340,916
Convertible Senior Notes 1.25 Percent Due 2020
Convertible Notes
Interest rate of debt (as a percent)	1.25%	1.25%	1.25%
Convertible Senior Notes 1.25 Percent Due 2020 \| Carrying Amount
Convertible Notes
Convertible senior notes	$ 16,608	$ 310,565