Cash, Cash Equivalents, and Restricted Cash - Reconciliation to Statements of Cash Flows (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 166,874	$ 179,878	$ 158,934	$ 198,119
Restricted cash	243,048	236,684	138,264	222,092
Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows	$ 409,922	$ 416,562	$ 297,198	$ 420,211