Commitments and Contingencies - Additional Information (Detail)				3 Months Ended
	Apr. 30, 2021 USD ($)	Mar. 31, 2021 USD ($) Loans	Mar. 15, 2021 USD ($)	Mar. 31, 2021 USD ($) Directors Loans
Commitments And Contingencies [Line Items]
Number of loans receivable | Loans		79		79
Number of independent directors entitled to annual compensation | Directors				5
Average Rate				100.00%
Loans Receivable [Member]
Commitments And Contingencies [Line Items]
Unfunded loan commitments		$ 3,500,000,000		$ 3,500,000,000
Average Rate				73.10%
Aggregate unfunded loan commitments		2,400,000,000		$ 2,400,000,000
Weighted-average future funding period				3 years 2 months 12 days
Five Independent Board of Directors [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation		$ 175,000		$ 175,000
Annual cash compensation paid in the form of deferred stock units				100,000
Annual cash compensation paid in cash				75,000
Five Independent Board of Directors [Member] | Amendment One [Member] | Subsequent Event [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	$ 10,000
Compensation and Corporate Governance Committees [Member] | Amendment One [Member] | Subsequent Event [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