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Summary of Significant Accounting Policies Short-Term Investments (Details) (USD $)
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Dec. 31, 2011
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Dec. 31, 2010
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Short-term Investments | $ 335,783,000 | $ 326,218,000 |
| Available-for-sale Securities, Debt Maturities, within One Year, Fair Value | 212,300,000 | 285,400,000 |
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Commercial Paper [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Short-term Investments | 156,574,000 | 163,400,000 |
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US Government and Government Agencies and Authorities [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Short-term Investments | 66,647,000 | 140,076,000 |
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Corporate Bonds and Asset Backed Securities [Domain]
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Short-term Investments | 16,432,000 | 22,742,000 |
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Mutual and Exchange Traded Funds [Domain]
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Short-term Investments | $ 96,130,000 | $ 0 |