Summary of Significant Accounting Policies - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 144,173	$ 128,408	$ 473,355	$ 19,674
Restricted cash	36,792	7,023	$ 7,331
Reserves for Settlement of Loan Acquisitions
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	36,500	41,000
Restricted Lockbox Accounts
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	7,800	3,600
Escrow Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 29,000	$ 3,400