Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

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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Basis of Presentation and Significant Accounting Policies - Financial Instruments and Convertible Senior Notes (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2014	Sep. 29, 2014
Convertible Senior Notes
Fair value of principal amount	$ 751,400
Convertible senior notes due October 2021
Convertible Senior Notes
Aggregate principal amount			$ 201,300	$ 201,300
Interest rate (as a percent)			3.00%	3.00%
Fair value of principal amount	751,400
Fair Value, Measurements, Recurring
Financial Assets and Liabilities Measured At Fair Value
Total assets	487,471	$ 766,186
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 1
Financial Assets and Liabilities Measured At Fair Value
Total assets	487,471	766,186
Money Market Funds \| Fair Value, Measurements, Recurring
Financial Assets and Liabilities Measured At Fair Value
Cash and cash equivalents	487,471	766,186
Money Market Funds \| Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 1
Financial Assets and Liabilities Measured At Fair Value
Cash and cash equivalents	$ 487,471	$ 766,186