Investments in Real Estate - Schedule of Details of Properties Acquired (Detail) (Parenthetical)	12 Months Ended
	Dec. 31, 2017 ft² Property
Real Estate Properties [Line Items]
Number of Properties	115
HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Number of industrial properties	38
Emory Point [Member]
Real Estate Properties [Line Items]
Area of retail space | ft²	124,000
Multifamily [Member]
Real Estate Properties [Line Items]
Number of Properties	48
Industrial [Member]
Real Estate Properties [Line Items]
Number of Properties	55
Various [Member] | Multifamily [Member] | TA Multifamily Portfolio [Member]
Real Estate Properties [Line Items]
Number of garden style properties	5
Number of Properties	6
Various [Member] | Multifamily [Member] | ACG II Multifamily Portfolio [Member]
Real Estate Properties [Line Items]
Number of garden style properties	4
Number of Properties	4
Various [Member] | Multifamily [Member] | Aston Multifamily Portfolio [Member]
Real Estate Properties [Line Items]
Number of Properties	12
Various [Member] | Industrial [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Number of Properties	38
Various [Member] | Industrial [Member] | Southeast Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Number of industrial properties	5
Number of Properties	5
Atlanta [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Percentage of leased property	38.00%
Chicago [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Percentage of leased property	23.00%
Houston [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Percentage of leased property	17.00%
Harrisburg [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Percentage of leased property	10.00%
Dallas [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Percentage of leased property	10.00%
Orlando [Member] | HS Industrial Portfolio [Member]
Real Estate Properties [Line Items]
Percentage of leased property	2.00%