Summary of Significant Accounting Policies - Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash	$ 226,625	$ 202,525	$ 206,364
Restricted cash, current and long-term	77,774	39,265	17,999
Total Cash and Restricted Cash	$ 304,399	$ 241,790	$ 224,363	$ 221,161