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)
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

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-Name Accounting Standards Codification
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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Glossary Convertible Security
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Contractual interest rate for funds borrowed, under the debt agreement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

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The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Glossary Financing Activities
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Basis of Presentation and Significant Accounting Policies - Financial Instruments and Convertible Senior Notes (Details) - USD ($) $ in Thousands	1 Months Ended
	Sep. 30, 2014	Mar. 31, 2016	Dec. 31, 2015	Sep. 29, 2014
Convertible senior notes due October 2021
Convertible Senior Notes
Proceeds from issuance of convertible notes	$ 201,300
Interest rate (as a percent)	3.00%			3.00%
Net carrying amount		$ 123,800
Fair value of principal amount		309,200
Fair Value, Measurements, Recurring
Financial Assets and Liabilities Measured At Fair Value
Total assets		300,020	$ 224,885
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 1
Financial Assets and Liabilities Measured At Fair Value
Total assets		300,020	224,885
Money Market Funds \| Fair Value, Measurements, Recurring
Financial Assets and Liabilities Measured At Fair Value
Cash and cash equivalents		300,020	224,885
Money Market Funds \| Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 1
Financial Assets and Liabilities Measured At Fair Value
Cash and cash equivalents		$ 300,020	$ 224,885