SCHEDULE III Investment property reconciliation (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Beginning balance	$ 1,794,605	$ 1,580,544	$ 1,565,700
Community and land acquisitions, including immediate improvements	302,487	167,326	0
Community expansion and development	13,424	5,931	3,462
Improvements, other	110,029	78,844	46,460
Asset impairment	0	1,584	0
Dispositions and other	43,240	36,456	35,078
Ending balance	$ 2,177,305	$ 1,794,605	$ 1,580,544