Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and Cash Equivalents	$ 19,782	$ 21,146	$ 18,998
Restricted Cash	48,579	25,336	7,503
Total Cash, Cash Equivalents and Restricted Cash	$ 68,361	$ 46,482	$ 26,501	$ 21,461