Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Summary of information for reportable segments
Rental Income	$ 928,846		$ 603,410		$ 539,911
Resident fees and services	456,085		51,006		0
Interest income	41,070		40,855		40,885
Other income	11,295		7,245		15,847
Total Revenues	1,437,296		702,516		596,643
Property Operating Expenses	383,870		86,465		48,965
Net Operating Income	1,053,426	[1]	616,051	[1]	547,678	[1]
Real Estate Depreciation/Amortization	423,605		202,543		164,923
Interest Expense	321,999		160,960		109,773
Total assets	14,924,606		9,451,734
Medical Facilities [Member]
Summary of information for reportable segments
Rental Income	306,516	[2]	220,506	[2]	181,802
Resident fees and services	0	[2]	0	[2]	0
Interest income	7,002	[2]	4,679	[2]	4,940
Other income	3,985	[2]	985	[2]	9,368
Total Revenues	317,503	[2]	226,170	[2]	196,110
Property Operating Expenses	69,728	[2]	53,844	[2]	48,965
Net Operating Income	247,775	[1],[2]	172,326	[1]	147,145	[1]
Real Estate Depreciation/Amortization	107,092	[2]	75,826	[2]	63,623
Interest Expense	31,467	[2]	24,926	[2]	20,584
Total assets	3,795,940	[2]	3,389,441	[2]
Non-segment/Corporate [Member]
Summary of information for reportable segments
Rental Income	0		0		0
Resident fees and services	0		0		0
Interest income	0		0		0
Other income	690		2,874		1,170
Total Revenues	690		2,874		1,170
Property Operating Expenses	0		0		0
Net Operating Income	690	[1]	2,874	[1]	1,170	[1]
Real Estate Depreciation/Amortization	0		0		0
Interest Expense	228,884		113,129		76,567
Total assets	263,475		224,981
Senior Housing Facilities Operating [Member]
Summary of information for reportable segments
Rental Income	0		0		0
Resident fees and services	456,085		51,006		0
Interest income	0		0		0
Other income	0		0		0
Total Revenues	456,085		51,006		0
Property Operating Expenses	314,142		32,621		0
Net Operating Income	141,943	[1]	18,385	[1]	0	[1]
Real Estate Depreciation/Amortization	138,192		15,504		0
Interest Expense	46,342		7,794		0
Total assets	3,041,238		1,080,416
Senior Housing Facilities Triple Net [Member]
Summary of information for reportable segments
Rental Income	622,330		382,904		358,109
Resident fees and services	0		0		0
Interest income	34,068		36,176		35,945
Other income	6,620		3,386		5,309
Total Revenues	663,018		422,466		399,363
Property Operating Expenses	0		0		0
Net Operating Income	663,018	[1]	422,466	[1]	399,363	[1]
Real Estate Depreciation/Amortization	178,321		111,213		101,300
Interest Expense	15,306		15,111		12,622
Total assets	$ 7,823,953		$ 4,756,896

[1] Net operating income (“NOI”) is used to evaluate the operating performance of our properties. We define NOI as total revenues, including tenant reimbursements, less property level operating expenses, which exclude depreciation and amortization, general and administrative expenses, impairments and interest expense. We believe NOI provides investors relevant and useful information because it measures the operating performance of our properties at the property level on an unleveraged basis. We use NOI to make decisions about resource allocations and to assess the property level performance of our properties.

[2] Excludes income and expense amounts related to our properties held in unconsolidated entities. Please see Note 7 for additional information