Supplemental Cash Flow Information (Schedule of Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 267,910	$ 207,867	$ 210,148
Restricted cash, Current	63,206	50,222	83,098
Restricted cash, Non-current		500,000
Cash, cash equivalents, and restricted cash	$ 331,116	$ 758,089	$ 293,246	$ 233,089