Fair Value Measurements - Assets Measured at Fair Value On A Recurring Basis (Details) (Fair Value, Measurements, Recurring [Member], Fair Value, Inputs, Level 1 [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
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	$ 59,458	$ 61,311
Cash equivalents	80,095	64,577
Total cash and cash equivalents	$ 139,553	$ 125,888