Rental Properties (Summary Of Carrying Amounts Of Rental Properties) (Details) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Real Estate Properties [Line Items]
Carrying amounts of rental properties	$ 2,189,838,000		$ 2,154,292,000
Accumulated depreciation	(355,945,000)		(335,116,000)
Total	1,833,893,000		1,819,176,000
Depreciation expense on rental properties	23,600,000	22,000,000
Building and improvements [Member]
Real Estate Properties [Line Items]
Carrying amounts of rental properties	1,654,885,000		1,602,676,000
Furniture, fixtures & equipment [Member]
Real Estate Properties [Line Items]
Carrying amounts of rental properties	43,011,000		54,737,000
Land [Member]
Real Estate Properties [Line Items]
Carrying amounts of rental properties	$ 491,942,000		$ 496,879,000