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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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+ References

No definition available.

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Convertible Notes - Carrying Amount and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Convertible Notes
Convertible senior notes	$ 16,608	$ 651,481
Carrying Amount
Convertible Notes
Convertible senior notes	24,001	651,481
Fair Value
Convertible Notes
Convertible senior notes	$ 49,560	$ 1,511,288
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 0.375 Percent Due 2018 \| Fair Value
Convertible Notes
Convertible senior notes	$ 14,129	$ 749,988
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
Convertible Senior Notes 1.25 Percent Due 2020 \| Fair Value
Convertible Notes
Convertible senior notes	$ 35,431	$ 761,300