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Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Financial assets subject to fair value measurements and the necessary disclosures
Number of pricing sources	2
Total available-for-sale securities	$ 348,397	$ 494,905
Money market funds | Recurring basis | Total.
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	168,847	132,364
Money market funds | Recurring basis | Level 1
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	168,847	132,364
U.S. government bonds and notes | Recurring basis | Total.
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	65,592	266,817
U.S. government bonds and notes | Recurring basis | Level 1
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities		48,604
U.S. government bonds and notes | Recurring basis | Level 2
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	65,592	218,213
Corporate notes, bonds and commercial paper | Recurring basis | Total.
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	113,958	95,724
Corporate notes, bonds and commercial paper | Recurring basis | Level 2
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	113,958	95,724
Recurring basis | Total.
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	348,397	494,905
Recurring basis | Level 1
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	168,847	180,968
Recurring basis | Level 2
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	179,550	313,937
Nonrecurring basis
Investment in non-marketable security
Carrying Value	2,000	2,000
Nonrecurring basis | Level 3
Investment in non-marketable security
Fair Value	2,000	2,000
Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	168,847	132,364
U.S. government bonds and notes
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	65,592	266,817
Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	$ 113,958	$ 95,724

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 12
-Subparagraph b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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=6379932&loc=d3e22054-111558

Reference 3: 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=6505594

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This item represents the aggregate carrying amount of all cost-method investments as reported on or included in the balance sheet. The original cost of the investments may differ from the aggregate carrying amount disclosed due to various adjustments such as: (i) dividends received in excess of earnings after the date of investment that are considered a return of investment and therefore recorded as reductions to cost of the investment, or (ii) a series of operating losses of an investee or other factors which may indicate that a decrease in value of the investment has occurred which is other than temporary and accordingly such decrease in value has been recognized.

+ 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 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6383889&loc=d3e40346-111594

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 18
-Paragraph 6
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6872867&loc=d3e40691-111596

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 03-1
-Paragraph 22
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 18
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Value of the not readily marketable security or category which has been determined by management based upon fair value methods, including pricing of similar securities and valuation techniques and is included in the schedule of financial condition or the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Chapter 7
-Paragraph 6-14
-IssueDate 2006-05-01
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 820
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6476668&loc=d3e45360-110995

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