Cash, Cash Equivalents, and Restricted Cash - Reconciliation to Statements of Cash Flows (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 130,037	$ 179,878	$ 134,441	$ 198,119
Restricted cash	253,603	236,684	153,781	222,092
Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows	$ 383,640	$ 416,562	$ 288,222	$ 420,211