Summary of Significant Accounting Policies - Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash	$ 203,189	$ 202,525
Restricted cash	40,139	39,265
Total Cash and Restricted Cash	$ 243,328	$ 241,790	$ 221,938	$ 224,363