Supplemental Cash Flow Information (Reconciliation of Cash, Cash Equivalents and Restricted Cash to Statement of Cash Flows) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 59,925	$ 64,982	$ 89,770
Restricted cash	3,519	2,651	3,343
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 63,444	$ 67,633	$ 93,113	$ 86,959