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 $) | Sep. 30, 2013 | Dec. 31, 2012 |
In Thousands, unless otherwise specified |
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) | | |