Business Segments (Details Textual) $ in Millions	6 Months Ended
	Jun. 30, 2015 USD ($) Units Property Segment	Jun. 30, 2014 USD ($)
Business Segments (Textual) [Abstract]
Number of reportable segments | Segment	2
Conventional Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Number of owned apartment communities in segments	143
Number of apartment homes in apartment communities | Units	41,425
Affordable Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Number of owned apartment communities in segments	56
Number of apartment homes in apartment communities | Units	8,685
Operating Segments [Member] | Conventional Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Capital additions related to segments | $	$ 156.6	$ 178.2
Operating Segments [Member] | Affordable Real Estate Operations [Member]
Business Segments (Textual) [Abstract]
Capital additions related to segments | $	$ 4.5	$ 3.6