Supplemental Cash Flow Information (Schedule of Cash, Cash Equivalents and Restricted Cash) (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	$ 278,944	$ 267,910
Restricted cash, Current	62,414	63,206
Cash, cash equivalents, and restricted cash	$ 341,358	$ 331,116	$ 874,880	$ 758,089