Summary of Significant Accounting Policies Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,112	$ 1,398	$ 45,923	$ 180,675
Restricted Cash	8,001	8,001	8,001	9,250
Restricted Cash and Cash Equivalents	$ 9,113	$ 9,399	$ 53,924	$ 189,925