Commitments and Contingencies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020 USD ($) Loans Directors	Dec. 31, 2019 USD ($)
Commitments And Contingencies [Line Items]
Number of loans receivable | Loans	94
Number of independent directors entitled to annual compensation | Directors	5
Loans Receivable [Member]
Commitments And Contingencies [Line Items]
Unfunded loan commitments	$ 3,905,323,000	$ 3,911,868,000
Average Rate	79.00%
Aggregate unfunded loan commitments	$ 2,400,000,000
Weighted-average future funding period	4 years
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