Segment Information - Additional Information (Detail) - 6 months ended Jun. 30, 2018	Total	Property	Communities	States
Segment Reporting Information [Line Items]
Number of owned or owned interests of apartment communities		304	303
Number of states in which apartment units are located				17
Period properties owned and stabilized	12 months
Occupancy Level for Stabilized Communities	90.00%
Period Properties Stabilized	90 days
Same Store [Member]
Segment Reporting Information [Line Items]
Period properties owned and stabilized	12 months