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FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2012 | Dec. 31, 2011
--- | --- | ---
Put options related to auction rate securities |  |
Fair value of certain assets |  |
Assets measured at fair value | $ 1,600 |
Level 1 |  |
Fair value of certain assets |  |
Cash | 112,725 | 81,879
Assets measured at fair value | 371,223 | 319,942
Level 1 | Money market funds |  |
Fair value of certain assets |  |
Assets measured at fair value | 258,096 | 230,029
Level 1 | U.S. Treasuries |  |
Fair value of certain assets |  |
Assets measured at fair value | 402 | 8,034
Level 2 |  |
Fair value of certain assets |  |
Assets measured at fair value | 439,803 | 438,013
Level 2 | Certificates of deposit |  |
Fair value of certain assets |  |
Assets measured at fair value | 42,197 | 69,078
Level 2 | Corporate bonds |  |
Fair value of certain assets |  |
Assets measured at fair value |  | 2,022
Level 2 | Municipal securities |  |
Fair value of certain assets |  |
Assets measured at fair value | 346,560 | 291,984
Level 2 | U.S. government agency securities. |  |
Fair value of certain assets |  |
Assets measured at fair value | 19,988 | 16,005
Level 2 | Variable rate demand notes |  |
Fair value of certain assets |  |
Assets measured at fair value | 31,058 | 58,924
Level 3 |  |
Fair value of certain assets |  |
Assets measured at fair value | 23,513 | 38,893
Level 3 | Auction rate securities |  |
Fair value of certain assets |  |
Assets measured at fair value | 21,864 | 35,852
Level 3 | Put options related to auction rate securities |  |
Fair value of certain assets |  |
Assets measured at fair value | 1,649 | 3,041
Total fair value |  |
Fair value of certain assets |  |
Cash | 112,725 | 81,879
Assets measured at fair value | 834,539 | 796,848
Total fair value | Money market funds |  |
Fair value of certain assets |  |
Assets measured at fair value | 258,096 | 230,029
Total fair value | U.S. Treasuries |  |
Fair value of certain assets |  |
Assets measured at fair value | 402 | 8,034
Total fair value | Certificates of deposit |  |
Fair value of certain assets |  |
Assets measured at fair value | 42,197 | 69,078
Total fair value | Corporate bonds |  |
Fair value of certain assets |  |
Assets measured at fair value |  | 2,022
Total fair value | Municipal securities |  |
Fair value of certain assets |  |
Assets measured at fair value | 346,560 | 291,984
Total fair value | U.S. government agency securities. |  |
Fair value of certain assets |  |
Assets measured at fair value | 19,988 | 16,005
Total fair value | Variable rate demand notes |  |
Fair value of certain assets |  |
Assets measured at fair value | 31,058 | 58,924
Total fair value | Auction rate securities |  |
Fair value of certain assets |  |
Assets measured at fair value | 21,864 | 35,852
Total fair value | Put options related to auction rate securities |  |
Fair value of certain assets |  |
Assets measured at fair value | $ 1,649 | $ 3,041

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- Definition Unrestricted cash available for day-to-day operating needs, for an entity that has cash equivalents, but does not aggregate cash equivalents with cash on the balance sheet. + 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 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -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 Cash -URI http://asc.fasb.org/extlink&oid=6506951 + Details
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