Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	$ 113,933,000	$ 28,485,000
Short-term Investments | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	42,451,000	4,647,000
Short-term Investments | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,149,000
Short-term Investments | US Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	26,463,000
Short-term Investments | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,997,000
Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	62,885,000	21,252,000
Long-term Investments | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	3,619,000
Long-term Investments | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	8,892,000
Long-term Investments | US Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7,764,000	2,070,000
Long-term Investments | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,992,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets, Fair Value Disclosure	266,044,000	139,071,000
Fair Value, Measurements, Recurring | Israeli Severance Funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Other assets	2,432,000	2,218,000
Fair Value, Measurements, Recurring | Cash Equivalents | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	49,750,000	86,166,000
Fair Value, Measurements, Recurring | Cash Equivalents | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	34,291,000	950,000
Fair Value, Measurements, Recurring | Cash Equivalents | U.S. dollar dominated foreign corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	1,003,000
Fair Value, Measurements, Recurring | Cash Equivalents | US Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	1,750,000
Fair Value, Measurements, Recurring | Short-term Investments | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	42,451,000	4,647,000
Fair Value, Measurements, Recurring | Short-term Investments | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	29,050,000	18,770,000
Fair Value, Measurements, Recurring | Short-term Investments | Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		5,068,000
Fair Value, Measurements, Recurring | Short-term Investments | Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	12,823,000
Fair Value, Measurements, Recurring | Short-term Investments | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,149,000
Fair Value, Measurements, Recurring | Short-term Investments | US Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	26,463,000
Fair Value, Measurements, Recurring | Short-term Investments | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,997,000
Fair Value, Measurements, Recurring | Long-term Investments | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	25,475,000	16,141,000
Fair Value, Measurements, Recurring | Long-term Investments | Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7,764,000	2,070,000
Fair Value, Measurements, Recurring | Long-term Investments | Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	15,143,000	3,041,000
Fair Value, Measurements, Recurring | Long-term Investments | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	3,619,000
Fair Value, Measurements, Recurring | Long-term Investments | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	8,892,000
Fair Value, Measurements, Recurring | Long-term Investments | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,992,000
Fair Value, Measurements, Recurring | 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	53,369,000	86,166,000
Fair Value, Measurements, Recurring | 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 | 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	49,750,000	86,166,000
Fair Value, Measurements, Recurring | 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 | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents | U.S. dollar dominated foreign corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents | US Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0
Fair Value, Measurements, Recurring | 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 | 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 | 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 | 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
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | 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 | 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 | 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 | 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	3,619,000
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets, Fair Value Disclosure	212,675,000	52,905,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Israeli Severance Funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Other assets	2,432,000	2,218,000
Fair Value, Measurements, Recurring | 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 | Significant Other Observable Inputs (Level 2) | Cash Equivalents | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	34,291,000	950,000
Fair Value, Measurements, Recurring | 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	1,003,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Cash Equivalents | US Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	1,750,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	42,451,000	4,647,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	29,050,000	18,770,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments | Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		5,068,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments | Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	12,823,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	1,149,000
Fair Value, Measurements, Recurring | 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	26,463,000
Fair Value, Measurements, Recurring | 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	1,997,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long-term Investments | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	25,475,000	16,141,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long-term Investments | Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7,764,000	2,070,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long-term Investments | Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	15,143,000	3,041,000
Fair Value, Measurements, Recurring | 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 | Significant Other Observable Inputs (Level 2) | Long-term Investments | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	8,892,000
Fair Value, Measurements, Recurring | 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	$ 1,992,000