Real Estate Properties (Details) (USD $)	12 Months Ended								3 Months Ended	12 Months Ended						1 Months Ended	12 Months Ended									1 Months Ended	12 Months Ended			12 Months Ended				12 Months Ended		1 Months Ended	12 Months Ended					12 Months Ended		1 Months Ended	12 Months Ended					12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended																																							1 Months Ended																																																																			1 Months Ended
	Dec. 31, 2012 item Property	Dec. 31, 2011 item	Dec. 31, 2010 item	Dec. 31, 2012 Five Star item	Dec. 31, 2011 Five Star	Dec. 31, 2010 Five Star	Dec. 31, 2012 Senior living communities Five Star item	Sep. 30, 2012 Senior living communities Five Star item	Sep. 30, 2012 Senior living communities Sunrise Senior Living, Inc. item	Dec. 31, 2012 Senior living communities Sunrise Senior Living, Inc.	Dec. 31, 2012 MOB	Dec. 31, 2011 MOB	Dec. 31, 2012 Acquisition Five Star	Dec. 31, 2011 Acquisition Five Star	Jul. 31, 2012 Acquisition Stellar Senior Living, LLC	Jul. 31, 2011 Acquisition Senior living communities	Dec. 31, 2012 Acquisition Senior living communities item	Dec. 31, 2011 Acquisition Senior living communities item	Dec. 31, 2012 Acquisition Senior Living Leased Community item	Dec. 31, 2011 Acquisition Senior Living Leased Community item	Dec. 31, 2012 Acquisition Senior Living Managed Community item	Dec. 31, 2011 Acquisition Senior Living Managed Community item	Dec. 31, 2012 Acquisition MOB item sqft	Dec. 31, 2011 Acquisition MOB item sqft	Dec. 31, 2012 Operations Transfer Agreement TRS item	May 31, 2012 Operations Transfer Agreement Five Star TRS item	Dec. 31, 2012 Operations Transfer Agreement Sunrise Senior Living, Inc. item	Dec. 31, 2012 Operations Transfer Agreement Senior living communities Sunrise Senior Living, Inc.	May 31, 2012 Operations Transfer Agreement Senior living communities Sunrise Senior Living, Inc. item	Dec. 31, 2012 Sale	Dec. 31, 2011 Sale	Dec. 31, 2012 Land	Dec. 31, 2011 Land	Dec. 31, 2012 Land Acquisition Senior Living Leased Community	Dec. 31, 2011 Land Acquisition Senior Living Leased Community	Dec. 31, 2011 Land Acquisition Senior Living Managed Community	Dec. 31, 2012 Land Acquisition Senior Living Managed Community	Dec. 31, 2012 Land Acquisition MOB	Dec. 31, 2011 Land Acquisition MOB	Dec. 31, 2012 Buildings and improvements	Dec. 31, 2011 Buildings and improvements	Dec. 31, 2012 Buildings and improvements Acquisition Senior Living Leased Community	Dec. 31, 2011 Buildings and improvements Acquisition Senior Living Leased Community	Dec. 31, 2011 Buildings and improvements Acquisition Senior Living Managed Community	Dec. 31, 2012 Buildings and improvements Acquisition Senior Living Managed Community	Dec. 31, 2012 Buildings and improvements Acquisition MOB	Dec. 31, 2011 Buildings and improvements Acquisition MOB	Dec. 31, 2012 Furniture, fixtures and equipment	Dec. 31, 2011 Furniture, fixtures and equipment	Dec. 31, 2012 Furniture, fixtures and equipment Acquisition Senior Living Leased Community	Dec. 31, 2011 Furniture, fixtures and equipment Acquisition Senior Living Leased Community	Dec. 31, 2011 Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Dec. 31, 2012 Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Feb. 29, 2012 Alabama Acquisition Senior Living Managed Community item	Feb. 29, 2012 Alabama Land Acquisition Senior Living Managed Community	Feb. 29, 2012 Alabama Buildings and improvements Acquisition Senior Living Managed Community	Feb. 29, 2012 Alabama Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Jul. 31, 2012 South Carolina Acquisition Senior Living Managed Community item	May 31, 2012 South Carolina Acquisition Senior Living Managed Community item	Jul. 31, 2012 South Carolina Land Acquisition Senior Living Managed Community	May 31, 2012 South Carolina Land Acquisition Senior Living Managed Community	Jul. 31, 2012 South Carolina Buildings and improvements Acquisition Senior Living Managed Community	May 31, 2012 South Carolina Buildings and improvements Acquisition Senior Living Managed Community	Jul. 31, 2012 South Carolina Furniture, fixtures and equipment Acquisition Senior Living Managed Community	May 31, 2012 South Carolina Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Jul. 31, 2012 Various Acquisition Senior Living Leased Community item	Jun. 30, 2011 Various Acquisition Senior Living Leased Community item	Dec. 31, 2011 Various Acquisition Senior Living Managed Community item	Jun. 30, 2011 Various Acquisition Senior Living Managed Community item	Sep. 30, 2011 Various Acquisition MOB item sqft	Jan. 31, 2011 Various Acquisition MOB item sqft	Jul. 31, 2012 Various Land Acquisition Senior Living Leased Community	Jun. 30, 2011 Various Land Acquisition Senior Living Leased Community	Dec. 31, 2011 Various Land Acquisition Senior Living Managed Community	Jun. 30, 2011 Various Land Acquisition Senior Living Managed Community	Sep. 30, 2011 Various Land Acquisition MOB	Jan. 31, 2011 Various Land Acquisition MOB	Jul. 31, 2012 Various Buildings and improvements Acquisition Senior Living Leased Community	Jun. 30, 2011 Various Buildings and improvements Acquisition Senior Living Leased Community	Dec. 31, 2011 Various Buildings and improvements Acquisition Senior Living Managed Community	Jun. 30, 2011 Various Buildings and improvements Acquisition Senior Living Managed Community	Sep. 30, 2011 Various Buildings and improvements Acquisition MOB	Jan. 31, 2011 Various Buildings and improvements Acquisition MOB	Jul. 31, 2012 Various Furniture, fixtures and equipment Acquisition Senior Living Leased Community	Jun. 30, 2011 Various Furniture, fixtures and equipment Acquisition Senior Living Leased Community	Dec. 31, 2011 Various Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Jun. 30, 2011 Various Furniture, fixtures and equipment Acquisition Senior Living Managed Community	May 31, 2011 Illinois Acquisition Senior Living Leased Community item	May 31, 2011 Illinois Land Acquisition Senior Living Leased Community	May 31, 2011 Illinois Buildings and improvements Acquisition Senior Living Leased Community	May 31, 2011 Illinois Furniture, fixtures and equipment Acquisition Senior Living Leased Community	Jul. 31, 2011 Florida Acquisition Five Star	Jul. 31, 2011 Florida Acquisition Senior Living Leased Community item	Aug. 31, 2011 Florida Acquisition Senior Living Managed Community item	Jul. 31, 2011 Florida Acquisition Senior Living Managed Community item	Jul. 31, 2012 Florida Acquisition MOB item sqft	Jul. 31, 2011 Florida Acquisition MOB item sqft	Jun. 30, 2011 Florida Acquisition MOB item sqft	Jul. 31, 2011 Florida Land Acquisition Senior Living Leased Community	Aug. 31, 2011 Florida Land Acquisition Senior Living Managed Community	Jul. 31, 2011 Florida Land Acquisition Senior Living Managed Community	Jul. 31, 2012 Florida Land Acquisition MOB	Jul. 31, 2011 Florida Land Acquisition MOB	Jun. 30, 2011 Florida Land Acquisition MOB	Jul. 31, 2011 Florida Buildings and improvements Acquisition Senior Living Leased Community	Aug. 31, 2011 Florida Buildings and improvements Acquisition Senior Living Managed Community	Jul. 31, 2011 Florida Buildings and improvements Acquisition Senior Living Managed Community	Jul. 31, 2012 Florida Buildings and improvements Acquisition MOB	Jul. 31, 2011 Florida Buildings and improvements Acquisition MOB	Jun. 30, 2011 Florida Buildings and improvements Acquisition MOB	Jul. 31, 2011 Florida Furniture, fixtures and equipment Acquisition Senior Living Leased Community	Aug. 31, 2011 Florida Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Jul. 31, 2011 Florida Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Aug. 31, 2012 New York Acquisition Senior Living Managed Community item	Aug. 31, 2012 New York Land Acquisition Senior Living Managed Community	Aug. 31, 2012 New York Buildings and improvements Acquisition Senior Living Managed Community	Aug. 31, 2012 New York Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Aug. 31, 2012 Missouri Acquisition Senior Living Managed Community item	Aug. 31, 2012 Missouri Land Acquisition Senior Living Managed Community	Aug. 31, 2012 Missouri Buildings and improvements Acquisition Senior Living Managed Community	Aug. 31, 2012 Missouri Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Dec. 31, 2012 Tennessee Acquisition Senior Living Managed Community item	Nov. 30, 2012 Tennessee Acquisition MOB item sqft	Oct. 31, 2012 Tennessee Acquisition MOB item	Dec. 31, 2012 Tennessee Land Acquisition Senior Living Managed Community	Nov. 30, 2012 Tennessee Land Acquisition MOB	Dec. 31, 2012 Tennessee Buildings and improvements Acquisition Senior Living Managed Community	Nov. 30, 2012 Tennessee Buildings and improvements Acquisition MOB	Dec. 31, 2012 Tennessee Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Dec. 31, 2012 Texas Acquisition Senior Living Managed Community item	Dec. 31, 2012 Texas Acquisition MOB item sqft	Jul. 31, 2012 Texas Acquisition MOB item sqft	Dec. 31, 2012 Texas Land Acquisition Senior Living Managed Community	Dec. 31, 2012 Texas Land Acquisition MOB	Jul. 31, 2012 Texas Land Acquisition MOB	Dec. 31, 2012 Texas Buildings and improvements Acquisition Senior Living Managed Community	Dec. 31, 2012 Texas Buildings and improvements Acquisition MOB	Jul. 31, 2012 Texas Buildings and improvements Acquisition MOB	Dec. 31, 2012 Texas Furniture, fixtures and equipment Acquisition Senior Living Managed Community	Dec. 31, 2011 California Acquisition Senior Living Managed Community item	Dec. 31, 2011 California Land Acquisition Senior Living Managed Community	Dec. 31, 2011 California Buildings and improvements Acquisition Senior Living Managed Community	Dec. 31, 2011 California Furniture, fixtures and equipment Acquisition Senior Living Managed Community	May 31, 2012 Georgia Acquisition MOB item sqft	May 31, 2012 Georgia Additional acquisition MOB item sqft	May 31, 2012 Georgia Land Acquisition MOB	May 31, 2012 Georgia Land Additional acquisition MOB	May 31, 2012 Georgia Buildings and improvements Acquisition MOB	May 31, 2012 Georgia Buildings and improvements Additional acquisition MOB	Jun. 30, 2012 Hawaii Acquisition MOB item sqft	Jun. 30, 2012 Hawaii Land Acquisition MOB	Jun. 30, 2012 Hawaii Buildings and improvements Acquisition MOB	Jun. 30, 2012 Maryland Acquisition MOB item sqft	Jun. 30, 2012 Maryland Land Acquisition MOB	Jun. 30, 2012 Maryland Buildings and improvements Acquisition MOB	Sep. 30, 2012 Massachusetts Acquisition MOB item sqft	Jul. 31, 2012 Massachusetts Sale MOB item sqft	Sep. 30, 2012 Massachusetts Land Acquisition MOB	Sep. 30, 2012 Massachusetts Buildings and improvements Acquisition MOB	Dec. 31, 2012 Minnesota Acquisition MOB item sqft	May 31, 2011 Minnesota Acquisition MOB item sqft	Jan. 31, 2011 Minnesota Acquisition MOB item sqft	Dec. 31, 2012 Minnesota Land Acquisition MOB	May 31, 2011 Minnesota Land Acquisition MOB	Jan. 31, 2011 Minnesota Land Acquisition MOB	Dec. 31, 2012 Minnesota Buildings and improvements Acquisition MOB	May 31, 2011 Minnesota Buildings and improvements Acquisition MOB	Jan. 31, 2011 Minnesota Buildings and improvements Acquisition MOB	Dec. 31, 2012 Colorado Acquisition MOB item sqft	Dec. 31, 2012 Colorado Land Acquisition MOB	Dec. 31, 2012 Colorado Buildings and improvements Acquisition MOB	Nov. 30, 2011 Virginia Acquisition MOB item sqft	Nov. 30, 2011 Virginia Land Acquisition MOB	Nov. 30, 2011 Virginia Buildings and improvements Acquisition MOB	Dec. 31, 2011 Indiana Acquisition MOB item sqft	Dec. 31, 2011 Indiana Land Acquisition MOB	Dec. 31, 2011 Indiana Buildings and improvements Acquisition MOB	Dec. 31, 2012 Pennsylvania Senior living communities	Dec. 31, 2011 Pennsylvania Senior living communities	Dec. 31, 2012 Pennsylvania Sale Senior living communities item	Feb. 28, 2013 Washington MOB item	Jan. 31, 2013 Washington Acquisition Senior living communities Living units item	Feb. 28, 2013 Washington Acquisition MOB sqft	Jan. 31, 2013 Mississippi Agreement to acquire MOB sqft
Real Estate Properties
Number of properties owned	392
Number of states in which properties are located	40
Real Estate Properties
Real estate properties, at cost	$ 5,183,307,000	$ 4,721,591,000																														$ 615,623,000	$ 564,628,000							$ 4,354,165,000	$ 3,969,086,000							$ 213,519,000	$ 187,877,000
Accumulated depreciation	750,903,000	630,261,000																																						645,585,000	543,064,000							105,318,000	87,197,000
Number of properties acquired or agreed to be acquired							39										11	28	4	6	7	22	13	28																														1				1	1							4	4	8	10	13	6																	1					1	1	2	1	1	3																1				1				1	1							1	2	1								1				1	1					1			1			1				1	1	1							2			2			1						2
Number of units																			511	679	948	3,187																																92				232	59							511	523	1,916	824																			73					83	121	269																			310				87				90								78										57																																										150
Number of acquisition agreements																																																																																																																												1
Aggregate purchase price of properties acquired, excluding closing costs											449,657,000	991,618,000				99,808,000			36,500,000	99,808,000	187,462,000	556,415,000	225,695,000	336,395,000																														11,300,000				37,273,000	8,059,000							36,500,000	82,073,000	379,000,000	114,521,000	167,000,000	95,870,000																	7,500,000					10,235,000	17,158,000	34,436,000	7,750,000	5,200,000	14,550,000																99,000,000				11,280,000				11,550,000	9,200,000							9,000,000	23,550,000	16,850,000								11,300,000				8,600,000	23,100,000					70,495,000			18,250,000			16,400,000				15,100,000	7,200,000	14,150,000							16,400,000			11,425,000			21,000,000							22,350,000	38,000,000	14,600,000
Intangible assets recorded related to acquisition																			1,900,000		6,626,000																																	583,000				1,762,000	362,000							1,900,000																																																2,726,000				330,000				428,000								435,000
Assumption of mortgage notes payable	121,793,000	217,317,000	2,458,000																6,876,000	11,458,000	41,814,000	192,573,000	73,103,000	13,286,000																																			4,789,000							6,876,000	11,458,000	130,752,000	36,605,000																									124,459,000	12,757,000		3,653,000																	31,187,000				5,838,000																																52,000,000						11,462,000				9,641,000												9,633,000										12,266,000
Premium on Assumed Debt																			628,000		3,439,000		1,862,000																																											628,000																																																2,747,000				692,000																																						1,008,000				854,000
Area of real estate properties acquired (in square feet)																							839,194	2,480,159																																														1,310,664	737,018																									52,858	32,321	125,990																									33,796								80,216	63,082												28,440	111,538					204,429			92,180			33,600	18,900			76,637	49,809	84,474							62,418			45,645			94,238								144,900	71,824
Intangible lease liabilities recorded	21,978,000	25,487,000																					971,000	3,770,000																																														1,919,000	1,600,000																											200,000																									50,000								11,000													10,000						629,000			78,000							183,000	51,000								10,000
Intangible lease assets recorded	161,419,000	130,153,000																					32,684,000	52,209,000																																														31,150,000	9,217,000																									789,000	354,000	599,000																									1,132,000								4,006,000	1,973,000												1,392,000	6,421,000					4,306,000			3,570,000			1,812,000				4,087,000	1,403,000	2,722,000							3,196,000			1,897,000			4,867,000
Property plant and equipment recorded																																		4,100,000	7,235,000	65,173,000	17,250,000	30,588,000	53,620,000			29,728,000	88,410,000	474,949,000	161,369,000	165,256,000	234,336,000			1,400,000	4,163,000	16,293,000	5,656,000		1,300,000	9,071,000	346,000			3,898,000	1,092,000	30,670,000	6,405,000	943,000	200,000							4,100,000	6,145,000	49,180,000	10,293,000	28,960,000	16,210,000	29,728,000	72,757,000	320,370,000	99,270,000	108,809,000	72,043,000	1,400,000	3,171,000	9,450,000	4,958,000		200,000	6,925,000	375,000								890,000	2,390,000	1,300,000	1,620,000	570,000	2,600,000	8,728,000	14,369,000	31,989,000	5,341,000	4,276,000	11,551,000	617,000	399,000	1,147,000		8,460,000	87,492,000	3,069,000		260,000	10,852,000	530,000				800,000	1,528,000	10,000,000	6,590,000	322,000				1,440,000	3,116,000	990,000	6,879,000	16,439,000	13,887,000	246,000		2,010,000	8,951,000	339,000			1,080,000	3,500,000	6,138,000	13,179,000		11,200,000	55,618,000		1,900,000	12,858,000			1,443,000	14,153,000				2,774,000	1,300,000	1,220,000	9,276,000	4,548,000	10,208,000		1,437,000	11,777,000		930,000	8,598,000		1,830,000	14,303,000
Number of properties acquired, referred to as managed properties				39			29
Number of real estate properties leased							10	188																	10				10
Number of properties under accelerated lease termination																											10
Number of communities under lease termination																										10
Number of lease communities remaining under termination									2
Gain on lease terminations	375,000									375,000
Rental income	460,811,000	422,166,000	340,113,000
Number of communities under management operations																										10
Payments to purchase the inventory and certain improvements owned by Sunrise	316,769,000	797,113,000	431,497,000																									1,000,000
Number of properties classified as held for sale	1																																																																																																																																																												1																							1
Real estate properties, held for sale																																																																																																																																																													1,100,000																					850,000	850,000
Loss on sale of properties	(101,000)	21,315,000	109,000																											(101,000)	21,315,000																																																																																																																														101,000
Impairment of asset charges recorded	3,071,000	1,990,000	5,965,000
Number of properties impaired	1	4	7
Real estate improvements purchased				30,520,000	33,269,000	31,894,000							30,520,000	33,269,000
Increase or decrease in annual lease rent payable				2,456,000	2,665,000	2,555,000							2,456,000	2,665,000
Annual lease rent payable															2,920,000																																																																													7,531,000																																																																																										1,732,000
Reductions in rental income on capitalized above market and below market lease due to amortization	(1,597,000)	93,000	(891,000)
Amortization expenses included in depreciation and amortization	19,340,000	11,318,000	4,468,000
Future minimum lease payments
2013	406,068,000
2014	389,755,000
2015	373,938,000
2016	356,626,000
2017	315,917,000
Thereafter	$ 2,421,860,000