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	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 134,987	$ 63,895	$ 96,734
Restricted Cash and Cash Equivalents, Current	0	4,040	11,219
Restricted Cash, Noncurrent	2,523		3,050
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 137,510	$ 70,867	$ 111,003	$ 116,941