Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and Cash Equivalents	$ 43,102	$ 21,146
Restricted Cash	7,271	25,336	$ 11,602
Total Cash, Cash Equivalents, Restricted Cash	$ 50,373	$ 46,482	$ 21,461	$ 26,992