Segment Information - Additional Information (Detail) individual in Millions	9 Months Ended
	Sep. 30, 2015 Property States individual
Segment Reporting Information [Line Items]
Number of owned or owned interests of apartment communities | Property	253
Number of states in which apartment units are located | States	15
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
Non Same Store And Other [Member]
Segment Reporting Information [Line Items]
Percentage of Total Public Multifamily REIT Units	1.00%