Business Segments (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Business Segments (Textual) [Abstract]
Number of reportable segments	2
Conventional Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Number of owned apartment communities in segments	141
Number of apartment homes in apartment communities	42,566
Affordable Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Number of owned apartment communities in segments	57
Number of apartment homes in apartment communities	8,769
Operating Segments [Member] | Conventional Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Capital additions related to segments	$ 61.3	$ 86.6
Operating Segments [Member] | Affordable Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Capital additions related to segments	$ 2.6	$ 1.7