Investments in Real Estate - Schedule of Purchase Price Allocation of Properties (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Real Estate Properties [Line Items]
Building and building improvements	$ 2,807,957
Land and land improvements	573,001
Furniture, fixtures and equipment	62,216
In-place lease intangibles	161,310
Intangible assets	159,916
Below-market lease intangibles	(15,189)
Other intangibles	676
Total purchase price	3,617,378
Assumed mortgage notes	200,967
Net purchase price	3,416,411
Below-market Ground Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	4,623
Above-market Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	6,670
Prepaid Ground Lease Rent [Member]
Real Estate Properties [Line Items]
Intangible assets	16,114
TA Multifamily Portfolio [Member]
Real Estate Properties [Line Items]
Building and building improvements	337,889
Land and land improvements	68,456
Furniture, fixtures and equipment	4,651
In-place lease intangibles	21,880
Below-market lease intangibles	(307)
Total purchase price	432,593
Net purchase price	432,593
TA Multifamily Portfolio [Member] | Above-market Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	24
HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Building and building improvements	345,391
Land and land improvements	45,081
In-place lease intangibles	20,793
Below-market lease intangibles	(8,061)
Total purchase price	405,930
Net purchase price	405,930
HS Industrial Portfolio [Member] | Above-market Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	2,726
Aston Multifamily Portfolio [Member]
Real Estate Properties [Line Items]
Building and building improvements	306,602
Land and land improvements	47,645
Furniture, fixtures and equipment	4,926
In-place lease intangibles	22,272
Total purchase price	381,445
Net purchase price	381,445
Emory Point [Member]
Real Estate Properties [Line Items]
Building and building improvements	171,709
Furniture, fixtures and equipment	3,040
In-place lease intangibles	11,207
Below-market lease intangibles	(576)
Total purchase price	201,578
Net purchase price	201,578
Emory Point [Member] | Above-market Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	84
Emory Point [Member] | Prepaid Ground Lease Rent [Member]
Real Estate Properties [Line Items]
Intangible assets	16,114
Nevada West Multifamily [Member]
Real Estate Properties [Line Items]
Building and building improvements	145,305
Land and land improvements	17,409
Furniture, fixtures and equipment	2,833
In-place lease intangibles	5,418
Total purchase price	170,965
Net purchase price	170,965
All Other [Member]
Real Estate Properties [Line Items]
Building and building improvements	1,501,061
Land and land improvements	394,410
Furniture, fixtures and equipment	46,766
In-place lease intangibles	79,740
Below-market lease intangibles	(6,245)
Other intangibles	676
Total purchase price	2,024,867
Assumed mortgage notes	200,967
Net purchase price	1,823,900
All Other [Member] | Below-market Ground Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	4,623
All Other [Member] | Above-market Lease Intangibles [Member]
Real Estate Properties [Line Items]
Intangible assets	$ 3,836