Investments in Unconsolidated Entities (Details) (USD $)	1 Months Ended	12 Months Ended
	Aug. 31, 2012 property	Dec. 31, 2012 property	Dec. 31, 2011 property	Dec. 31, 2010
Equity method investments
Number of properties accounted for under equity method		55	92
Management fees earned in connection with unconsolidated entities		$ 7,300,000	$ 5,700,000	$ 1,900,000
Net investments in unconsolidated entities		95,409,000	105,303,000
Income (loss) from unconsolidated entities		18,154,000	(52,000)	(664,000)
Number of businesses acquired	36
Number of businesses acquired marketed for sale	1
Purchase of joint ventures	350,000,000	1,587,068,000
Notes payable and other debt	101,600,000
Purchase price of acquisition of assets	380,000,000
investment in joint ventures	12,500,000
Fair value of previously held equity interest	30,000,000
Gain on re-measurement of equity method investments	$ 16,600,000
Minimum
Equity method investments
Ownership interests in properties accounted for under the equity method (as a percent)		5.00%
Ownership interest acquired (as a percent)	80.00%
Maximum
Equity method investments
Ownership interests in properties accounted for under the equity method (as a percent)		25.00%
Ownership interest acquired (as a percent)	95.00%
ATRIA
Equity method investments
Ownership interests in properties accounted for under the equity method (as a percent)		34.00%