Investments in Real Estate-Related Securities - Summary of Investments in CMBS (Detail) $ in Thousands	Jun. 30, 2017 USD ($) Investment
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fair Value	$ 291,549
Commercial Mortgage Backed Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Investments | Investment	12
Face Amount	$ 289,871
Cost Basis	289,914
Fair Value	$ 291,549
Commercial Mortgage Backed Securities [Member] | BBB Credit Rating [Member] | Office, Industrial, Hospitality [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Investments | Investment	4
Face Amount	$ 114,659
Cost Basis	114,659
Fair Value	$ 115,307
Commercial Mortgage Backed Securities [Member] | BBB Credit Rating [Member] | Office, Industrial, Hospitality [Member] | Three-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	2.15%
Commercial Mortgage Backed Securities [Member] | BB Credit Rating [Member] | Office, Hospitality, Multifamily [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Investments | Investment	5
Face Amount	$ 150,899
Cost Basis	150,942
Fair Value	$ 151,800
Commercial Mortgage Backed Securities [Member] | BB Credit Rating [Member] | Office, Hospitality, Multifamily [Member] | Three-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	3.29%
Commercial Mortgage Backed Securities [Member] | B Credit Rating [Member] | Office, Multifamily [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Number of Investments | Investment	3
Face Amount	$ 24,313
Cost Basis	24,313
Fair Value	$ 24,442
Commercial Mortgage Backed Securities [Member] | B Credit Rating [Member] | Office, Multifamily [Member] | Three-Month U.S. Dollar-Denominated London Interbank Offer Rate [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted Average Coupon	3.79%