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Investments in Partially Owned Entities - Summary of Companys Investment in Unconsolidated Entities (Parenthetical) (Details)
 12 Months Ended
Dec. 31, 2018
ApartmentUnit
JointVenture
Jun. 30, 2019
ApartmentUnit
Variable Interest Entity [Line Items]    
Apartment units   79,624
Operating Property [Member] | Unconsolidated Non-VIE [Member]    
Variable Interest Entity [Line Items]    
Apartment units 945  
Number of joint ventures under agreements | JointVenture 2