Investments in Real Estate Debt - Summary of Investments in Real Estate Debt (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) Position	Dec. 31, 2019 USD ($) Position
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	217	203
Weighted Average Coupon	3.20%	4.40%
Weighted Average Maturity Date	May 11, 2025	Sep. 21, 2025
Cost Basis	$ 5,168,122	$ 4,493,288
Fair Value	$ 4,649,372	$ 4,523,260
Total Real Estate Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	207	195
Weighted Average Coupon	3.10%	4.20%
Weighted Average Maturity Date	Nov. 05, 2025	Oct. 15, 2025
Cost Basis	$ 4,442,374	$ 4,185,744
Fair Value	$ 3,941,724	$ 4,216,055
Total Real Estate Loans [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	10	8
Weighted Average Maturity Date	Aug. 24, 2022	Oct. 16, 2024
Face Amount/ Notional	$ 738,908	$ 309,989
Cost Basis	725,748	307,544
Fair Value	$ 707,648	$ 307,205
Total Real Estate Loans [Member] | One-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	3.70%	4.60%
Commercial Mortgage Backed Securities Floating
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	125	122
Weighted Average Maturity Date	Feb. 05, 2025	Jan. 29, 2025
Face Amount/ Notional	$ 3,130,665	$ 2,907,080
Cost Basis	3,121,193	2,899,556
Fair Value	$ 2,723,768	$ 2,906,952
Commercial Mortgage Backed Securities Floating | One-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	2.70%	2.70%
Commercial Mortgage Backed Securities Fixed
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	50	43
Weighted Average Coupon	4.10%	4.20%
Weighted Average Maturity Date	Aug. 19, 2027	Jun. 26, 2027
Face Amount/ Notional	$ 912,705	$ 850,738
Cost Basis	889,144	829,403
Fair Value	$ 795,728	$ 831,970
Commercial Mortgage Backed Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	5	5
Weighted Average Coupon	2.30%	2.30%
Weighted Average Maturity Date	Oct. 01, 2026	Oct. 02, 2026
Face Amount/ Notional	$ 2,259,760	$ 2,261,480
Cost Basis	21,691	23,564
Fair Value	$ 21,680	$ 23,547
Mezzanine Loan [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	1	1
Weighted Average Maturity Date	Dec. 15, 2024	Dec. 15, 2024
Face Amount/ Notional	$ 134,750	$ 134,750
Cost Basis	134,251	134,078
Fair Value	$ 116,384	$ 134,076
Mezzanine Loan [Member] | One-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	6.90%	6.90%
Commercial Mortgage Backed Securities Zero Coupon [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	4	4
Weighted Average Maturity Date	Jan. 30, 2027	Dec. 30, 2026
Face Amount/ Notional	$ 236,090	$ 236,090
Cost Basis	132,318	127,219
Fair Value	$ 138,741	$ 136,027
Term Loans [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	9	7
Weighted Average Maturity Date	Mar. 11, 2022	Aug. 30, 2024
Face Amount/ Notional	$ 604,158	$ 175,239
Cost Basis	591,497	173,466
Fair Value	$ 591,264	$ 173,129
Term Loans [Member] | One-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	3.00%	2.90%
Residential Mortgage Backed Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	10	9
Weighted Average Coupon	4.40%	4.30%
Weighted Average Maturity Date	Dec. 06, 2031	Jul. 09, 2028
Face Amount/ Notional	$ 26,141	$ 29,315
Cost Basis	26,315	29,506
Fair Value	$ 24,084	$ 29,448
Corporate Bond [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Positions | Position	13	12
Weighted Average Coupon	5.10%	5.20%
Weighted Average Maturity Date	Jan. 02, 2027	Feb. 16, 2027
Face Amount/ Notional	$ 252,492	$ 276,302
Cost Basis	251,713	276,496
Fair Value	$ 237,723	$ 288,111