v2.4.1.9
Financial Instruments and Fair Value Measurements , Fair Value Measurements (Details) (Recurring [Member], USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Estimate of Fair Value [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total Assets, Fair Value Disclosure $ 715,367us-gaap_AssetsFairValueDisclosure
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$ 721,801us-gaap_AssetsFairValueDisclosure
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Estimate of Fair Value [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total Assets, Fair Value Disclosure 31,155us-gaap_AssetsFairValueDisclosure
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15,309us-gaap_AssetsFairValueDisclosure
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Estimate of Fair Value [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total Assets, Fair Value Disclosure 684,212us-gaap_AssetsFairValueDisclosure
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706,492us-gaap_AssetsFairValueDisclosure
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Estimate of Fair Value [Member] | Corporate debt securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 568,806us-gaap_AvailableForSaleSecurities
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589,016us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Corporate debt securities [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Corporate debt securities [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 568,806us-gaap_AvailableForSaleSecurities
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589,016us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 43,750us-gaap_AvailableForSaleSecurities
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51,155us-gaap_AvailableForSaleSecurities
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= us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember
Estimate of Fair Value [Member] | Commercial paper [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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0us-gaap_AvailableForSaleSecurities
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= us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember
Estimate of Fair Value [Member] | Commercial paper [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 43,750us-gaap_AvailableForSaleSecurities
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51,155us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Municipal bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 49,820us-gaap_AvailableForSaleSecurities
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39,721us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Municipal bonds [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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0us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Municipal bonds [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 49,820us-gaap_AvailableForSaleSecurities
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39,721us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Certificates of deposit and term deposits [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 13,080us-gaap_AvailableForSaleSecurities
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22,854us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 13,080us-gaap_AvailableForSaleSecurities
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22,854us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 29,154us-gaap_AvailableForSaleSecurities
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13,311us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Money market funds [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 29,154us-gaap_AvailableForSaleSecurities
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13,311us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | Money market funds [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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0us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | U.S. government and agency securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 10,757us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
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5,744us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | U.S. government and agency securities [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 2,001us-gaap_AvailableForSaleSecurities
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1,998us-gaap_AvailableForSaleSecurities
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Estimate of Fair Value [Member] | U.S. government and agency securities [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 8,756us-gaap_AvailableForSaleSecurities
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3,746us-gaap_AvailableForSaleSecurities
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Reported as [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total Assets, Fair Value Disclosure 715,367us-gaap_AssetsFairValueDisclosure
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721,801us-gaap_AssetsFairValueDisclosure
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Reported as [Member] | Cash equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 29,154us-gaap_AvailableForSaleSecurities
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13,311us-gaap_AvailableForSaleSecurities
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Reported as [Member] | Short-term investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure 417,605us-gaap_AvailableForSaleSecurities
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436,766us-gaap_AvailableForSaleSecurities
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Reported as [Member] | Long-term investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities, Fair Value Disclosure $ 268,608us-gaap_AvailableForSaleSecurities
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$ 271,724us-gaap_AvailableForSaleSecurities
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/ us-gaap_FairValueByMeasurementBasisAxis
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