Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) Loans
Commitments And Contingencies [Line Items]
Number of loans receivable | Loans	84
Average Rate	100.00%
Loans Receivable [Member]
Commitments And Contingencies [Line Items]
Unfunded loan commitments	$ 3,200,000,000
Average Rate	72.80%
Aggregate unfunded loan commitments	$ 2,200,000,000
Weighted-average future funding period	3 years 8 months 12 days
Five Independent Board of Directors [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	$ 175,000
Annual cash compensation paid in the form of deferred stock units	100,000
Annual cash compensation paid in cash	75,000
Chairperson of Audit Committee [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	20,000
Audit Committee Members [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	10,000
Compensation and Corporate Governance Committees [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	$ 10,000