Loans Held for Investment and the Allowance for Credit Losses - Summary of Loan Portfolio Activity (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Loans And Leases Receivable Disclosure [Line Items]
Loans and leases receivable loans sold		$ 85,500
Total loan commitment amount	$ 4,943,511	4,943,511	$ 5,628,765
Extinguishment of unpaid principal balance		112,000
PIK interest	800	4,700
One Loan
Loans And Leases Receivable Disclosure [Line Items]
Loans and leases receivable unpaid principal balance	78,400	78,400
Principal balance sales, realized loss		13,800
Loans and leases receivable expected initial unpaid principal balance	99,300	99,300
Subordinated and Mezzanine Loans
Loans And Leases Receivable Disclosure [Line Items]
Loans and leases receivable loans sold		46,400
Total loan commitment amount	50,000	50,000
First Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Loans and leases receivable unpaid principal balance	279,200	279,200
Total loan commitment amount	300,800	300,800
Extinguishment of unpaid principal balance		112,000
Fair value of property	$ 99,200	99,200
Principal balance sales, realized loss		12,800
Additional Fundings
Loans And Leases Receivable Disclosure [Line Items]
PIK interest		4,800
Collection of Principal
Loans And Leases Receivable Disclosure [Line Items]
PIK interest		$ 100