Supplemental Cash Flow Information (Reconciliation of Cash, Cash Equivalents and Restricted Cash to Statement of Cash Flows) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Information
Cash and cash equivalents	$ 65,490	$ 35,594	$ 55,110
Restricted cash	3,322	4,877	2,564
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 68,812	$ 40,471	$ 57,674	$ 67,633