Marketable Securities and Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Marketable securities and fair value measurements
Amortized cost	$ 90,203
Gross Unrealized Gains	40
Gross Unrealized Losses	(88)
Estimated Fair Value	90,155
Long-term
Marketable securities and fair value measurements
Amortized cost	78,775
Gross Unrealized Gains	37
Gross Unrealized Losses	(82)
Estimated Fair Value	78,730
Short-term
Marketable securities and fair value measurements
Amortized cost	11,428
Gross Unrealized Gains	3
Gross Unrealized Losses	(6)
Estimated Fair Value	11,425
Recurring basis
Marketable securities and fair value measurements
Total assets	325,328	$ 362,897
Recurring basis \| Cash equivalents
Marketable securities and fair value measurements
Money market funds	195,173	302,595
Recurring basis \| Short-term
Marketable securities and fair value measurements
Certificates of deposit	40,000	60,000
Investment securities	11,425
Recurring basis \| Long-term
Marketable securities and fair value measurements
Investment securities	78,730
Recurring basis \| Restricted cash
Marketable securities and fair value measurements
Money market funds		302
Recurring basis \| Level 1
Marketable securities and fair value measurements
Total assets	235,173	362,897
Recurring basis \| Level 1 \| Cash equivalents
Marketable securities and fair value measurements
Money market funds	195,173	302,595
Recurring basis \| Level 1 \| Short-term
Marketable securities and fair value measurements
Certificates of deposit	40,000	60,000
Recurring basis \| Level 1 \| Restricted cash
Marketable securities and fair value measurements
Money market funds		$ 302
Recurring basis \| Level 2
Marketable securities and fair value measurements
Total assets	90,155
Recurring basis \| Level 2 \| Short-term
Marketable securities and fair value measurements
Investment securities	11,425
Recurring basis \| Level 2 \| Long-term
Marketable securities and fair value measurements
Investment securities	$ 78,730

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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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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+ 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 210.5-02.2)

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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+ References

No definition available.

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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 Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

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Reference 5: 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 7

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Fair value portion of short to medium-term investment available at banks and savings and loan institutions where a customer agrees to lend money to the institution for a certain amount of time and is paid a predetermined rate of interest. Certificates of deposit (CD) are typically Federal Deposit Insurance Corporation (FDIC) insured.

+ References

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Fair value portion of fund that invests in short-term money-market instruments.

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