Real Estate Acquisitions and Dispositions Real Estate Acquisitions and Dispositions - Additional Information (Details)	Dec. 31, 2016 ft² Apartments	Sep. 30, 2016 ft² a Apartments	Jun. 30, 2016 a Apartments
Retreat at West Creek II [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land | a			11.0
Colonial Promenade Craft Farms
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²		30
Area of Land | a		295,447.00
River's Walk [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land | a		25.0
1201 Midtown [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property	302
The Denton II [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land | a		30,000.00
CV at Stone Point [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		192
CG at Autumn Park [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		402
Colonial Village at Woodlake [Member]
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²	266
Colonial Village at Tradewinds [Member]
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²	284
Colonial Village at Harbour Club [Member]
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²	213
Colonial Village at Main Park [Member]
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²	192
Lane At Towne Crossing [Member]
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²	384
Cobblestone Square [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property			314
Corners at Crystal Lake [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		240
Glen Eagles [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		310
Colonial Village at Greystone [Member]
Significant Acquisitions and Disposals [Line Items]
Square footage of real estate property (square foot) | ft²		408
CV at Mill Creek [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		220
Abbington Place [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		152
Colonial Promenade Huntsville [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land | a			1.30
Residences at Fountainhead [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property			322
Yale at 6th [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		352
Innovation Apartment Homes [Member]
Significant Acquisitions and Disposals [Line Items]
Number of units in real estate property		336