Summary of Significant Accounting Policies Supplemental Cash Flow Disclosure (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 243,684	$ 198,850
Current restricted cash	5,716	7,007
Restricted Cash and Cash Equivalents, Noncurrent	1,745	1,727
Restricted Cash and Cash Equivalents	7,461	8,734
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 251,145	$ 207,584	$ 170,973	$ 340,601