Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) | Jun. 30, 2015 | Dec. 31, 2014 |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | $ 434,950,000 | $ 402,679,000 |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | 539,366,000 | 509,514,000 |
Fair Value, Measurements, Recurring [Member] | Israeli Severance Funds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Other assets | 2,396,000 | 2,307,000 |
Fair Value, Measurements, Recurring [Member] | Cash Equivalents | Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Cash equivalents | 69,376,000 | 80,786,000 |
Fair Value, Measurements, Recurring [Member] | Cash Equivalents | Commercial paper | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Cash equivalents | 32,644,000 | 21,997,000 |
Fair Value, Measurements, Recurring [Member] | Cash Equivalents | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Cash equivalents | | 1,745,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 276,789,000 | 254,787,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Commercial paper | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 23,113,000 | 33,998,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 154,583,000 | 151,966,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | | 901,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government agency bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 62,249,000 | 41,587,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government treasury bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 23,606,000 | 15,777,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Agency discount notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 3,000,000 | |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | | 1,398,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 10,238,000 | 9,160,000 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | | 1,398,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 158,161,000 | 147,892,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 65,911,000 | 57,089,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 517,000 | 521,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government agency bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 39,523,000 | 48,217,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Foreign bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 517,000 | 521,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government treasury bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 35,811,000 | 20,813,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 7,159,000 | 9,551,000 |
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 9,240,000 | 11,701,000 |
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 | 128,793,000 | 117,376,000 |
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 | 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 | 69,376,000 | 80,786,000 |
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) | Cash Equivalents | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Cash equivalents | | 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 | | |
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 | U.S. government 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) | Short-term Investments | U.S. government treasury bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 23,606,000 | 15,777,000 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments | Agency discount notes [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 | Certificates of deposit | | |
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 | | |
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 | U.S. dollar dominated foreign corporate 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) | Long-term Investments | U.S. government 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 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | U.S. government treasury bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 35,811,000 | 20,813,000 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments | Municipal securities | | |
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 | Asset-backed securities | | |
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 | 410,573,000 | 392,138,000 |
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 | 2,396,000 | 2,307,000 |
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 | 32,644,000 | 21,997,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Cash Equivalents | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Cash equivalents | | 1,745,000 |
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 | 23,113,000 | 33,998,000 |
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 | 154,583,000 | 151,966,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | | 901,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | U.S. government agency bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 62,249,000 | 41,587,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | U.S. government treasury bonds | | |
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) | Short-term Investments | Agency discount notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 3,000,000 | |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | | 1,398,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Short-term Investments | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 10,238,000 | 9,160,000 |
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 | 65,911,000 | 57,089,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | U.S. dollar dominated foreign corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 517,000 | |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | U.S. government agency bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 39,523,000 | 48,217,000 |
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 | | 521,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | U.S. government treasury bonds | | |
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) | Long-term Investments | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | 7,159,000 | 9,551,000 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Long-term Investments | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Investments | $ 9,240,000 | $ 11,701,000 |