Cash and Cash Equivalents and Investments (Details 1) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents
Fair Value
Amortized Cost	$ 61,674	$ 137,266
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	61,674	137,266
Certificates of Deposit
Fair Value
Amortized Cost	553	552
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	553	552
U.S. Treasury Securities
Fair Value
Amortized Cost	191,231	201,584
Gross Unrealized Gains	59	3
Gross Unrealized Losses	0	(66)
Estimated Fair Value	191,290	201,521
Corporate Debt Securities
Fair Value
Amortized Cost	2,906
Gross Unrealized Gains	0
Gross Unrealized Losses	(1)
Estimated Fair Value	2,905
Total Short-term Investments
Fair Value
Amortized Cost	194,690	202,136
Gross Unrealized Gains	59	3
Gross Unrealized Losses	(1)	(66)
Estimated Fair Value	194,748	202,073
Total Cash and Cash Equivalents and Investments
Fair Value
Amortized Cost	256,364	339,402
Gross Unrealized Gains	59	3
Gross Unrealized Losses	(1)	(66)
Estimated Fair Value	$ 256,422	$ 339,339

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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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 investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 45

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-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26626-111562

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