Consolidated Statements of Cash Flows - Supplemental Information (Reconciliation 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 Elements [Abstract]
Cash and cash equivalents	$ 148,929	$ 35,687	$ 2,003
Restricted cash	56,816	15,634	4,304
Total cash, cash equivalents, and restricted cash	$ 205,745	$ 51,321	$ 6,307	$ 5,042