Organization (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2018 shares	Dec. 31, 2018 community	Dec. 31, 2018 building	Dec. 31, 2018	Dec. 31, 2018 investment	Dec. 31, 2018 apartment	Dec. 31, 2018 project
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General partner ownership interest	96.60%	96.70%
Limited partner - ownership percentage		3.40%				3.40%
Operating Partnership units outstanding (in shares) | shares		2,268,114	2,305,389
Redemption value of Operating Partnership units outstanding | $	$ 565.3	$ 547.5
Number of apartment communities owned | community				245
Number of apartment units owned | apartment								59,661
Ownership interests, number of commercial buildings | building					1
Ownership interests, number of active development projects							2		6