Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 278,782	$ 388,490	$ 305,890
Restricted cash	203,633	201,300	175,557
Total Cash and cash equivalents and Restricted cash shown in the Consolidated Statements of Cash Flows	$ 482,415	$ 589,790	$ 481,447	$ 532,782