Subsequent Events (Details) (USD $) Share data in Thousands, unless otherwise specified	9 Months Ended				0 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Common Stock	Sep. 30, 2011 Common Stock	Oct. 16, 2012 Subsequent Blackstone JV Senior housing item	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Minimum	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Maximum	Oct. 19, 2012 Subsequent Blackstone JV Senior housing Common Stock	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Real Estate Secured item	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Assisted living	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Independent living	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Memory care	Oct. 16, 2012 Subsequent Blackstone JV Senior housing Skilled nursing
Subsequent Events
Number of senior housing communities					133
Purchase price of agreed acquisition					$ 17,300,000,000
Number of states where acquired senior housing communities are located					29
Number of units					10,350
Percentage of units of real estate property										61.00%	25.00%	13.00%	1.00%
Number of communities that are stabilized					99
Number of communities currently lease-up					34
Rental and related revenues					105,500,000
Rate of increase in rent receivable per year after each of the next four years of initial lease term (as a percent)						3.70%
Rate of increase in rent receivable per year for remaining years of lease term (as a percent)						3.00%
Percentage of operating leases basis spread on variable floor rate						103.00%
Percentage of operating leases basis spread on variable cap rate						130.00%
Number of asset pools					3
Initial available term of asset pools						14 years	16 years
Initial lease term with Emeritus Corporation					5 years
Number of extension options with Emeritus Corporation					2
Total initial available term of asset pools						30 years	35 years
Principal amount of secured debt									52,000,000
Term of loan									4 years
Interest rate on debt, initially (as a percent)									6.10%
Interest rate on debt after four year term (as a percent)									7.05%
Number of senior housing facilities purchased									9
Issuance of common stock, net	761,070,000	1,288,332,000	19,096,000	36,256,000
Issuance of common stock, net (in shares)			19,096	36,256				22,000
Proceeds from issuance of common stock								$ 979,000,000