Investments in Real Estate Debt - Summary of Collateral Type of Properties Securing 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%
Hospitality [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	84	75
Cost Basis	$ 2,199,573	$ 2,252,556
Fair Value	$ 1,960,694	$ 2,259,102
Percentage Based on Fair Value	40.00%	50.00%
Multifamily [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	71	61
Cost Basis	$ 991,973	$ 596,184
Fair Value	$ 1,015,850	$ 613,470
Percentage Based on Fair Value	21.00%	14.00%
Office [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	38	37
Cost Basis	$ 766,733	$ 793,782
Fair Value	$ 715,184	$ 794,881
Percentage Based on Fair Value	14.00%	18.00%
Industrial [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	24	14
Cost Basis	$ 669,778	$ 375,975
Fair Value	$ 656,682	$ 378,147
Percentage Based on Fair Value	13.00%	8.00%
Diversified [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	17	10
Cost Basis	$ 314,077	$ 219,215
Fair Value	$ 297,011	$ 219,798
Percentage Based on Fair Value	6.00%	5.00%
Other [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	5	5
Cost Basis	$ 238,202	$ 238,202
Fair Value	$ 201,398	$ 240,558
Percentage Based on Fair Value	4.00%	5.00%
Net Lease [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	1
Cost Basis	$ 99,820
Fair Value	$ 102,942
Percentage Based on Fair Value	2.00%
Retail [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	1	1
Cost Basis	$ 17,375	$ 17,374
Fair Value	$ 15,916	$ 17,304