Summary of Significant Accounting Policies - Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash	$ 245,604	$ 226,625
Restricted cash, current and long-term	64,330	77,774
Total Cash and Restricted Cash	$ 309,934	$ 304,399	$ 243,328	$ 241,790