Cash and Cash Equivalents and Fair Value of Financial Instruments - Assets Measured at Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 60,103	$ 64,577
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	60,103	64,577
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash	27,925	61,311
Money market funds	60,103	64,577
Total cash and cash equivalents	$ 88,028	$ 125,888