Supplemental Cash Flow Information (Reconciliation of Cash, Cash Equivalents and Restricted Cash to Statement of Cash Flows) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 55,110	$ 64,982	$ 82,953
Restricted Cash and Cash Equivalents	2,564	2,651	2,852
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 57,674	$ 67,633	$ 85,805	$ 86,959