Commitments and Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2021 USD ($) Loans Directors
Commitments And Contingencies [Line Items]
Number of loans receivable | Loans	108
Number of independent directors entitled to annual compensation | Directors	6
Loans Receivable [Member]
Commitments And Contingencies [Line Items]
Unfunded loan commitments	$ 4,200,000,000
Aggregate unfunded loan commitments	$ 2,600,000,000
Weighted-average future funding period	3 years 2 months 12 days
Unfunded Commitments Related To Loans Receivable Excluding Identified Financing	$ 1,600,000,000
Five Independent Board of Directors [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	210,000
Annual cash compensation paid in the form of deferred stock units	115,000
Annual cash compensation paid in cash	95,000
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
Compensation and Corporate Governance Committees [Member] | Amendment One [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	15,000
Investment risk management committee [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	$ 7,500