Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Restricted cash	$ 13,842	$ 20,959	$ 22,905	$ 27,662
Lender Reserves [Member]
Cash and Cash Equivalents [Line Items]
Restricted cash	11,800	18,800
Restricted Lockbox Accounts [Member]
Cash and Cash Equivalents [Line Items]
Restricted cash	$ 2,000	$ 2,200