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	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 111,898	$ 63,895	$ 120,195
Restricted Cash and Cash Equivalents, Current	3,992	4,040	0
Restricted Cash, Noncurrent	2,989		2,909
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 118,879	$ 70,867	$ 123,104	$ 116,941