Fair Value Measurement - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Cash Equivalents, at Carrying Value [Abstract]
Cash equivalents	$ 23,975	$ 60,618	$ 31,583
Cash	164,172	195,343	114,875
Total cash and cash equivalents	$ 188,147	$ 255,961	$ 146,458	$ 229,121