Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) (USD $) | Mar. 31, 2014 | Dec. 31, 2013 |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | $322,606,000 | $229,018,000 |
Fair Value, Measurements, Recurring [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Assets, Fair Value Disclosure | 415,403,000 | 390,149,000 |
Fair Value, Measurements, Recurring [Member] | Israeli Severance Funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Other assets | 2,274,000 | 2,193,000 |
Fair Value, Measurements, Recurring [Member] | Cash Equivalents | Money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 55,518,000 | 143,540,000 |
Fair Value, Measurements, Recurring [Member] | Cash Equivalents | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 32,995,000 | 15,398,000 |
Fair Value, Measurements, Recurring [Member] | Cash Equivalents | U.S. dollar dominated foreign corporate bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 2,010,000 | ' |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 183,677,000 | 127,040,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 67,341,000 | 54,328,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 59,310,000 | 29,085,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. dollar dominated foreign corporate bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 8,108,000 | 13,971,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Agency bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 22,805,000 | 16,703,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Foreign bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 8,108,000 | ' |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | US Treasury and Government [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 2,546,000 | ' |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Municipal Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 9,626,000 | 7,014,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | US Government Agency Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 22,805,000 | 16,703,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Asset-backed Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 13,941,000 | 5,939,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 138,929,000 | 101,978,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 45,836,000 | 23,313,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. dollar dominated foreign corporate bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 13,768,000 | 19,495,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Agency bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 31,084,000 | 38,118,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Foreign bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 13,768,000 | 19,495,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | US Treasury and Government [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 20,612,000 | 6,919,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Municipal Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 7,128,000 | 8,331,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | US Government Agency Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | ' | 6,919,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Asset-backed Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 20,501,000 | 5,802,000 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Assets, Fair Value Disclosure | 76,130,000 | 150,459,000 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Israeli Severance Funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Other assets | 0 | ' |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents | Money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 55,518,000 | 143,540,000 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | U.S. dollar dominated foreign corporate bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | ' | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | Foreign bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | ' |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | Municipal Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | US Government Agency Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | Asset-backed Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | Agency bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | Foreign bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | US Treasury and Government [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 20,612,000 | ' |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | Municipal Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | US Government Agency Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | ' | 6,919,000 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | Asset-backed Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Assets, Fair Value Disclosure | 339,273,000 | 239,690,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Israeli Severance Funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Other assets | 2,274,000 | 2,193,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Cash Equivalents | Money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Cash Equivalents | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 32,995,000 | 15,398,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Cash Equivalents | U.S. dollar dominated foreign corporate bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 2,010,000 | ' |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 67,341,000 | 54,328,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 59,310,000 | 29,085,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | U.S. dollar dominated foreign corporate bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | ' | 13,971,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Foreign bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 8,108,000 | ' |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | US Treasury and Government [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 2,546,000 | ' |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Municipal Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 9,626,000 | 7,014,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | US Government Agency Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 22,805,000 | 16,704,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Asset-backed Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 13,941,000 | 5,938,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 45,836,000 | 23,313,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | Agency bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 31,084,000 | 38,118,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | Foreign bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 13,768,000 | 19,495,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | US Treasury and Government [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 0 | ' |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | Municipal Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | 7,128,000 | 8,331,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | US Government Agency Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | ' | 0 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | Asset-backed Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Investments | $20,501,000 | $5,802,000 |