| **Financial Instruments and Fair Value Measurements - Fair Value Hierarchy (Details) (Recurring basis, USD $)In Thousands, unless otherwise specified** | Mar. 31, 2014 | Dec. 31, 2013 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total                                                                                                                                                   | $ 498,860     | $ 148,733     |
| Level 1                                                                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total                                                                                                                                                   | 441,912       | 126,710       |
| Level 2                                                                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total                                                                                                                                                   | 56,948        | 22,023        |
| Level 3                                                                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total                                                                                                                                                   | 0             | 0             |
| Money market funds                                                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 7,073         | 1,761         |
| Money market funds | Level 1                                                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 7,073         | 1,761         |
| Money market funds | Level 2                                                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 0             | 0             |
| Money market funds | Level 3                                                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 0             | 0             |
| U.S. Treasury securities                                                                                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 209,997       |          |
| Investments, fair value                                                                                                                                 | 224,842       | 124,949       |
| U.S. Treasury securities | Level 1                                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 209,997       |          |
| Investments, fair value                                                                                                                                 | 224,842       | 124,949       |
| U.S. Treasury securities | Level 2                                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 0             |          |
| Investments, fair value                                                                                                                                 | 0             | 0             |
| U.S. Treasury securities | Level 3                                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Cash and cash equivalents, fair value                                                                                                                   | 0             |          |
| Investments, fair value                                                                                                                                 | 0             | 0             |
| Corporate debt securities                                                                                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 53,575        | 22,023        |
| Corporate debt securities | Level 1                                                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 0             | 0             |
| Corporate debt securities | Level 2                                                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 53,575        | 22,023        |
| Corporate debt securities | Level 3                                                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 0             | 0             |
| Preferred stock                                                                                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 3,373         |          |
| Preferred stock | Level 1                                                                                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 0             |          |
| Preferred stock | Level 2                                                                                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | 3,373         |          |
| Preferred stock | Level 3                                                                                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Investments, fair value                                                                                                                                 | $ 0           |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
+ References
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=25499696&loc=d3e19207-110258
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ 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=6506951Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016
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| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560
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