Segment Information - Additional Information (Detail) - 9 months ended Sep. 30, 2017 individual in Millions	Total	Property	States	Communities	individual
Segment Reporting Information [Line Items]
Number of owned or owned interests of apartment communities		303		302
Number of states in which apartment units are located | States			17
Period properties owned and stabilized	12 months
Occupancy Level for Stabilized Communities	90.00%
Period Properties Stabilized	90 days
Large Market Same Store [Member]
Segment Reporting Information [Line Items]
Apartment Community Population					1
Percentage of Total Public Multifamily REIT Units	1.00%
Period properties owned and stabilized	12 months
Secondary Market Same Store [Member]
Segment Reporting Information [Line Items]
Apartment Community Population					1
Percentage of Total Public Multifamily REIT Units	1.00%
Period properties owned and stabilized	12 months