Investment Property (Details) (USD $)			1 Months Ended		1 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Countryside Atlanta [Member]	Sep. 30, 2009 Countryside Atlanta [Member] sites	Dec. 31, 2011 Reidsville, North Carolina [Member] sites
Real estate, investment property [Line Items]
Land	$ 153,412,000	$ 140,230,000
Land improvements and buildings	1,358,006,000	1,342,325,000
Rental homes and improvements	263,549,000	246,245,000
Furniture, fixtures, and equipment	41,826,000	41,172,000
Land held for future development	25,606,000	24,633,000
Investment property	1,842,399,000	1,794,605,000
Accumulated depreciation	(613,191,000)	(597,999,000)
Investment property, net	1,229,208,000	1,196,606,000
Number of units in real estate property destroyed (in sites)				109
Insurance Recoveries			4,800,000
Impairment charges					$ 1,400,000
Number of sites (in sites)					45
Number of potential expansion units in real estate property (in sites)					145