Investments in Real Estate Debt - Summary of Credit Rating of Investments in Real Estate Debt (Detail) $ in Thousands	Sep. 30, 2020 USD ($) Position	Dec. 31, 2019 USD ($) Position
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	241	203
Cost Basis	$ 5,297,531	$ 4,493,288
Fair Value	$ 4,965,677	$ 4,523,260
Percentage Based on Fair Value	100.00%	100.00%
BB Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	79	72
Cost Basis	$ 1,632,234	$ 1,598,930
Fair Value	$ 1,503,362	$ 1,610,643
Percentage Based on Fair Value	30.00%	36.00%
Non Rated [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	38	33
Cost Basis	$ 1,177,793	$ 764,941
Fair Value	$ 1,149,268	$ 773,791
Percentage Based on Fair Value	23.00%	17.00%
B Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	52	40
Cost Basis	$ 1,220,773	$ 906,609
Fair Value	$ 1,130,536	$ 909,587
Percentage Based on Fair Value	23.00%	20.00%
BBB Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	51	45
Cost Basis	$ 883,408	$ 885,891
Fair Value	$ 812,313	$ 891,272
Percentage Based on Fair Value	16.00%	20.00%
A Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	15	10
Cost Basis	$ 341,495	$ 319,031
Fair Value	$ 331,143	$ 320,140
Percentage Based on Fair Value	7.00%	7.00%
CCC Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	3
Cost Basis	$ 32,429
Fair Value	$ 29,665
Percentage Based on Fair Value	1.00%
AAA Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	2	2
Cost Basis	$ 8,608	$ 9,554
Fair Value	$ 8,600	$ 9,550
AA Credit Rating [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	1	1
Cost Basis	$ 791	$ 8,332
Fair Value	$ 790	$ 8,277