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
Restricted Cash [Abstract]
Restricted Cash and Cash Equivalents, Noncurrent	$ 1,727	$ 1,937
Restricted Cash and Cash Equivalents	8,734	10,562
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	207,584	340,601	$ 211,506	$ 151,093
Restricted Cash, Current	7,007	8,625
Cash and cash equivalents	$ 198,850	$ 330,039