Description of Business and Summary of Significant Accounting Policies Cash, Cash Equivalents, and Restricted Cash Shown in the Statement of Cash Flows (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 113,410	$ 63,895	$ 68,449
Restricted Cash and Cash Equivalents, Current	3,992	4,040	3,998
Restricted Cash, Noncurrent	2,591		2,855
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 119,993	$ 70,867	$ 75,302	$ 116,941