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Investments and Fair Value Measurements (Details) (USD $)
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Sep. 30, 2012
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Dec. 31, 2011
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|---|---|---|
| Assets: | ||
| Maturity period of liquid investments, maximum (in months) | P3M | |
| Maturity period of short term investments, minimum (in months) | P3M | |
| Maturity period of short term investments, maximum (in years) | P1Y | |
| Number of securities with unrealized position | 1 | 2 |
| Period of continuous unrealized loss position, minimum (in years) | P1Y | P1Y |
| Estimated fair value of securities in gross unrealized loss position | $ 5,000,000 | $ 12,600,000 |
| Gross unrealized loss on securities in continuous unrealized loss position | 100,000 | 200,000 |
| Gross unrealized gains | 900,000 | |
| Unrealized gain on investments | 835,000 | 450,000 |
| Unrealized gains and losses [Abstract] | ||
| Amortized Cost | 60,974,000 | |
| Gross Unrealized Gains | 657,000 | |
| Gross Unrealized Losses | (207,000) | |
| Estimated Fair Value | 61,424,000 | |
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Recurring [Member]
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| Assets: | ||
| Cash and cash equivalents | 44,989,000 | 14,848,000 |
| Fair value of assets | 91,880,000 | 78,357,000 |
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Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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| Assets: | ||
| Cash and cash equivalents | 44,989,000 | 14,848,000 |
| Fair value of assets | 91,880,000 | 73,096,000 |
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Recurring [Member] | Quoted Prices in Inactive Markets for Identical Assets (Level 2) [Member]
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| Assets: | ||
| Cash and cash equivalents | 0 | 0 |
| Fair value of assets | 0 | 5,261,000 |
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Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
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| Assets: | ||
| Cash and cash equivalents | 0 | 0 |
| Fair value of assets | 0 | 0 |
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Mutual funds [Member]
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| Unrealized gains and losses [Abstract] | ||
| Amortized Cost | 43,924,000 | 55,718,000 |
| Gross Unrealized Gains | 857,000 | 652,000 |
| Gross Unrealized Losses | (22,000) | (207,000) |
| Estimated Fair Value | 44,759,000 | 56,163,000 |
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Mutual funds [Member] | Recurring [Member]
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| Assets: | ||
| Fair value of investments | 44,759,000 | 56,163,000 |
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Mutual funds [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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| Assets: | ||
| Fair value of investments | 44,759,000 | 56,163,000 |
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Mutual funds [Member] | Recurring [Member] | Quoted Prices in Inactive Markets for Identical Assets (Level 2) [Member]
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| Assets: | ||
| Fair value of investments | 0 | 0 |
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Mutual funds [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
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| Assets: | ||
| Fair value of investments | 0 | 0 |
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Government agency bonds [Member]
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| Unrealized gains and losses [Abstract] | ||
| Amortized Cost | 5,256,000 | |
| Gross Unrealized Gains | 5,000 | |
| Gross Unrealized Losses | 0 | |
| Estimated Fair Value | 5,261,000 | |
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Government agency bonds [Member] | Recurring [Member]
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| Assets: | ||
| Fair value of investments | 5,261,000 | |
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Government agency bonds [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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| Assets: | ||
| Fair value of investments | 0 | |
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Government agency bonds [Member] | Recurring [Member] | Quoted Prices in Inactive Markets for Identical Assets (Level 2) [Member]
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| Assets: | ||
| Fair value of investments | 5,261,000 | |
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Government agency bonds [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
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| Assets: | ||
| Fair value of investments | 0 | |
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Certificate of deposit [Member] | Recurring [Member]
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| Assets: | ||
| Fair value of investments | 2,132,000 | 2,085,000 |
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Certificate of deposit [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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| Assets: | ||
| Fair value of investments | 2,132,000 | 2,085,000 |
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Certificate of deposit [Member] | Recurring [Member] | Quoted Prices in Inactive Markets for Identical Assets (Level 2) [Member]
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| Assets: | ||
| Fair value of investments | 0 | 0 |
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Certificate of deposit [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
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| Assets: | ||
| Fair value of investments | $ 0 | $ 0 |