Fair Value Measurements - Assets measured at fair value on a recurring basis and whose carrying values approximate their respective fair values (Details) (Fair value on recurring basis, USD $)
In Thousands, unless otherwise specified

Sep. 30, 2013

Dec. 31, 2012

Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Total assets measured at fair value

$ 73,370

$ 69,060

Fair Value Measurement, Significant Other Observable Inputs (Level 2)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Total assets measured at fair value

Fair Value Measurement, Significant Unobservable Inputs (Level 3)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Total assets measured at fair value

Corporate debt securities | Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Corporate debt securities, fair value

2,962

2,010

Corporate debt securities | Fair Value Measurement, Significant Other Observable Inputs (Level 2)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Corporate debt securities, fair value

Corporate debt securities | Fair Value Measurement, Significant Unobservable Inputs (Level 3)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Corporate debt securities, fair value

Money market funds (included in cash and cash equivalents) | Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Money market funds (included in cash and cash equivalents)

70,408

67,050

Money market funds (included in cash and cash equivalents) | Fair Value Measurement, Significant Other Observable Inputs (Level 2)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Money market funds (included in cash and cash equivalents)

Money market funds (included in cash and cash equivalents) | Fair Value Measurement, Significant Unobservable Inputs (Level 3)

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Money market funds (included in cash and cash equivalents)