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Segment Information Segment Information - Additional Information (Detail) - 12 months ended Dec. 31, 2017
Total
Property
States
Communities
Segment Reporting Information [Line Items]        
Number of Real Estate Properties   302   301
Number of states in which apartment units are located (states)     17  
Period properties owned and stabilized (months) 12 months      
Occupancy Level for Stabilized Communities 90.00%      
Period Properties Stabilized 90 days