Summary of Significant Accounting Policies - Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash	$ 215,706	$ 202,525
Restricted cash, current and long-term	54,697	39,265
Total Cash and Restricted Cash	$ 270,403	$ 241,790	$ 232,945	$ 224,363