Summary of Significant Accounting Policies Supplemental Cash Flow Disclosure (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 153,694	$ 198,850
Current restricted cash	4,964	7,007
Restricted Cash and Cash Equivalents, Noncurrent	1,736	1,727
Restricted Cash and Cash Equivalents	6,700	8,734
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 160,394	$ 207,584	$ 227,320	$ 340,601