Real Estate - Acquisitions (Details) - 2019 Acquisitions $ in Thousands				9 Months Ended
	Jul. 23, 2019 USD ($) unit	Jun. 27, 2019 USD ($) unit	Apr. 30, 2019 USD ($) unit	Sep. 30, 2019 USD ($) unit
Real Estate [Line Items]
Number of Units | unit				2,390
Contract Purchase Price | $				$ 530,920
Multifamily | Assembly Portfolio - Virginia
Real Estate [Line Items]
Number of Units | unit			1,685
Contract Purchase Price | $			$ 379,100
Multifamily | Assembly Portfolio - Maryland
Real Estate [Line Items]
Number of Units | unit		428
Contract Purchase Price | $		$ 82,070
Multifamily | Cascade at Landmark
Real Estate [Line Items]
Number of Units | unit	277
Contract Purchase Price | $	$ 69,750