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Marketable Securities (Details) (USD $) | 6 Months Ended |
--- | --- | ---
Jun. 30, 2011 | Dec. 31, 2010
Marketable Securities |  |
Maximum maturity period of available for sale securities (in years) | 3 |
Cash equivalents and marketable securities |  |
Fair Value | $ 348,397,000 | $ 494,905,000
Amortized Cost | 348,436,000 | 494,977,000
Gross Unrealized Gains | 25,000 | 37,000
Gross Unrealized Losses | (64,000) | (109,000)
Cash, fair value | 10,957,000 | 17,104,000
Cash | 10,957,000 | 17,104,000
Cash, cash equivalents and marketable securities |  |
Fair Value | 359,354,000 | 512,009,000
Amortized Cost | 359,393,000 | 512,081,000
Gross Unrealized Gains | 25,000 | 37,000
Gross Unrealized Losses | (64,000) | (109,000)
Fair value of Marketable debt securities which have insignificant unrealized losses and will mature within one year | 91,400,000 |
Contractual maturity: |  |
Due within one year | 348,397,000 | 494,905,000
Unrealized Loss, net |  |
Due within one year | (39,000) | (72,000)
Money market funds |  |
Cash equivalents and marketable securities |  |
Fair Value | 168,847,000 | 132,364,000
Amortized Cost | 168,847,000 | 132,364,000
Weighted Rate of Return (as a percent) | 0.01% | 0.04%
U.S. government bonds and notes |  |
Cash equivalents and marketable securities |  |
Fair Value | 65,592,000 | 266,817,000
Amortized Cost | 65,569,000 | 266,840,000
Gross Unrealized Gains | 23,000 | 29,000
Gross Unrealized Losses |  | (52,000)
Weighted Rate of Return (as a percent) | 0.22% | 0.26%
Corporate notes, bonds and commercial paper |  |
Cash equivalents and marketable securities |  |
Fair Value | 113,958,000 | 95,724,000
Amortized Cost | 114,020,000 | 95,773,000
Gross Unrealized Gains | 2,000 | 8,000
Gross Unrealized Losses | (64,000) | (57,000)
Weighted Rate of Return (as a percent) | 0.40% | 0.39%
Cash equivalents |  |
Cash equivalents and marketable securities |  |
Fair Value | 168,847,000 | 198,158,000
Short term marketable securities |  |
Cash equivalents and marketable securities |  |
Fair Value | $ 179,550,000 | $ 296,747,000

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