Organization (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2017 community	Dec. 31, 2017 building	Dec. 31, 2017	Dec. 31, 2017 investment	Dec. 31, 2017 apartment	Dec. 31, 2017 project
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General partner ownership interest	96.70%	96.70%
Limited partner - ownership percentage		3.30%				3.30%
Operating Partnership units outstanding (in shares) | shares	2,268,114	2,237,290
Redemption value of Operating Partnership units outstanding | $		$ 520.2	$ 547.5
Number of apartment communities owned | community				247
Apartment units owned | apartment								60,239
Ownership interests, number of commercial buildings | building					1
Ownership interests, number of active development projects							2		7