Rental Properties (Summary Of Carrying Amounts Of Rental Properties) (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Real Estate Properties [Line Items]
Carrying amounts of rental properties	$ 2,262,044,000		$ 2,154,292,000
Accumulated depreciation	(369,854,000)		(335,116,000)
Total	1,892,190,000		1,819,176,000
Depreciation expense on rental properties	36,100,000	33,100,000
Building and improvements [Member]
Real Estate Properties [Line Items]
Carrying amounts of rental properties	1,721,187,000		1,602,676,000
Furniture, fixtures & equipment [Member]
Real Estate Properties [Line Items]
Carrying amounts of rental properties	43,723,000		54,737,000
Land [Member]
Real Estate Properties [Line Items]
Carrying amounts of rental properties	$ 497,134,000		$ 496,879,000