Fair Value Measurements - Assets measured at fair value on a recurring basis (Details) (Fair value on recurring basis, USD $) | Mar. 31, 2015 | Dec. 31, 2014 |
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 | $35,855 | $35,767 |
Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Corporate debt securities | 925 | 1,428 |
Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds (included in cash and cash equivalents) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Money market funds (included in cash and cash equivalents) | 34,930 | 34,339 |
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 Other Observable Inputs (Level 2) | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Corporate debt securities | | |
Fair Value Measurement, Significant Other Observable Inputs (Level 2) | Money market funds (included in cash and cash equivalents) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
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] | | |
Total assets measured at fair value | | |
Fair Value Measurement, Significant Unobservable Inputs (Level 3) | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Corporate debt securities | | |
Fair Value Measurement, Significant Unobservable Inputs (Level 3) | Money market funds (included in cash and cash equivalents) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Money market funds (included in cash and cash equivalents) | | |