Basis of Presentation and Summary of Significant Accounting Polices - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 174,242	$ 30,115	$ 39,940
Restricted cash	137,353	87,354	155,470
Total cash, cash equivalents, and restricted cash in the Consolidated Statements of Cash Flows	311,595	117,469	$ 195,410	$ 99,817
Average vault cash balance	$ 4,000,000	$ 3,200,000