v2.4.0.6

Fair Value Measurements (Details) (Recurring basis, USD $) In Thousands, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010
--- | --- | ---
Quoted Prices in Active markets for Identical Assets, Level 1 |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | $ 163,501 | $ 176,851
Quoted Prices in Active markets for Identical Assets, Level 1 | U.S. government securities |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 66,174 | 25,976
Quoted Prices in Active markets for Identical Assets, Level 1 | U.S. government agency securities |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 55,901 | 24,375
Quoted Prices in Active markets for Identical Assets, Level 1 | U.S. corporate notes |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 2,705 | 34,695
Quoted Prices in Active markets for Identical Assets, Level 1 | Money market funds |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 38,721 | 91,805
Significant Other Observable Inputs, Level 2 |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 72,250 | 127,494
Significant Other Observable Inputs, Level 2 | U.S. government agency securities |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 37,274 | 30,273
Significant Other Observable Inputs, Level 2 | U.S. commercial paper |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 34,976 | 97,221
Total |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 235,751 | 304,345
Total | U.S. government securities |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 66,174 | 25,976
Total | U.S. government agency securities |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 93,175 | 54,648
Total | U.S. corporate notes |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 2,705 | 34,695
Total | U.S. commercial paper |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | 34,976 | 97,221
Total | Money market funds |  |
Estimated fair values of entity's financial assets |  |
Fair value of financial assets | $ 38,721 | $ 91,805

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- Definition 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 investment securities as of the balance sheet date which may include 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=6505594 Reference 2: 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=6379932&loc=d3e22054-111558 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 -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 -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -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 SEC -Name Regulation S-X (SX) -Number 210 -Article 7 -Section 03 -Paragraph 1 -Subparagraph a, f, g Reference 7: 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=6956420&loc=d3e24584-111560 + Details
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