Cash and Cash Equivalents - Breakdown of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Money market funds	$ 31,688	$ 54,188
Interest-bearing bank deposits	88,091	114,127
Cash and cash equivalents	150,538	185,222
Total Cash and cash equivalents	$ 270,317	$ 353,537	$ 351,827	$ 323,181