Real Estate Properties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended			1 Months Ended				43 Months Ended	10 Months Ended	1 Months Ended		5 Months Ended	6 Months Ended	1 Months Ended
	Jun. 30, 2013	Dec. 31, 2014 property sqft building	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2014 property	Aug. 31, 2013 property	May 31, 2011 property	Dec. 31, 2014 property	Oct. 31, 2014 property	Dec. 31, 2013 property	Jan. 31, 2015 property sqft	Dec. 31, 2013 property	Sep. 30, 2014 property building	Oct. 31, 2014	Jun. 30, 2014 property item	Jan. 31, 2014	Feb. 28, 2015 item	Jan. 31, 2013 property item	Feb. 28, 2013 property sqft	May 31, 2014 property sqft	Apr. 30, 2014 property sqft	Oct. 31, 2013 property item	Nov. 30, 2013 property item	Mar. 31, 2013 property sqft
Real Estate Properties
Real estate properties, at cost		$ 6,238,611	$ 5,263,625			$ 6,238,611			6,238,611		5,263,625		$ 5,263,625
Accumulated depreciation		(983,850)	(840,760)			(983,850)			(983,850)		(840,760)		(840,760)
Assumption of mortgage notes payable		15,630	12,266	121,793
Impairment of asset charges recorded	32,267	(10)	7,989	3,071
Number of properties classified as held for sale		5				5			5
Number of buildings classified as held for sale		8				8			8
Number of properties impaired		5
Gain on the sale of property		5,453	37,392	(101)
Intangible lease assets recorded		577,177	166,247			577,177			577,177		166,247		166,247
Intangible lease liabilities recorded		138,469	22,170			138,469			138,469		22,170		22,170
Reductions in rental income on capitalized above market and below market lease due to amortization		2,322	(3,656)	(1,597)
Amortization expenses included in depreciation and amortization		38,970	22,718	19,340
Expenditure committed relating to leases		13,883
Area of real estate properties leased (in square feet)		750,000
Committed but unspent tenant related obligations		12,444
Future minimum lease payments
2015		475,705				475,705			475,705
2016		465,664				465,664			465,664
2017		446,673				446,673			446,673
2018		416,539				416,539			416,539
2019		385,874				385,874			385,874
Thereafter		2,796,142				2,796,142			2,796,142
Future amortization of intangible lease assets and liabilities
2015		39,438				39,438			39,438
2016		37,037				37,037			37,037
2017		33,362				33,362			33,362
2018		28,668				28,668			28,668
2019		25,802				25,802			25,802
Thereafter		185,655				185,655			185,655
Above market lease
Real Estate Properties
Intangible lease assets recorded		47,107	44,279			47,107			47,107		44,279		44,279
Accumulated amortization on lease assets		22,749	16,148			22,749			22,749		16,148		16,148
Weighted average amortization period		5 years 3 months 18 days
In-place lease intangibles
Real Estate Properties
Intangible lease assets recorded		530,070	121,968			530,070			530,070		121,968		121,968
Accumulated amortization on lease assets		81,640	46,605			81,640			81,640		46,605		46,605
Weighted average amortization period		12 years 9 months 18 days
Below market lease
Real Estate Properties
Accumulated amortization on lease assets		15,643	9,642			15,643			15,643		9,642		9,642
Weighted average amortization period		13 years 4 months 24 days
Five Star
Real Estate Properties
Real estate improvements purchased		25,804	27,208	30,520
Increase or decrease in annual lease rent payable		2,066	2,177	2,456	(9,500)
MOBs
Real Estate Properties
Number of properties classified as held for sale		1	4			1			1		4		4
Number of buildings classified as held for sale		7	7			7			7		7		7
Property held for sale (in square feet)		323,541	831,499			323,541			323,541		831,499		831,499
Number of properties impaired		4
Senior living communities
Real Estate Properties
Number of living units		312	744			312			312		744		744
Impairment of asset charges recorded		4,377	1,304
Number of properties classified as held for sale		4	10			4			4		10		10
Real estate properties, held for sale		3,551	27,888			3,551			3,551		27,888		27,888
Senior living communities | Five Star
Real Estate Properties
Number of properties acquired or agreed to be acquired		46				2		6	36
Number of properties acquired, referred to as managed properties		46
Cash Paid plus Assumed Debt, excluding closing costs						47,430
Number of properties to be sold							1
Increase or decrease in annual lease rent payable							(255)
Skilled nursing facilities
Real Estate Properties
Number of properties to be sold										3
Assisted living facility member
Real Estate Properties
Number of properties to be sold										3
Rehabilitation hospitals | Five Star
Real Estate Properties
Number of properties to be sold											2
Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Number of properties acquired or agreed to be acquired			1
Number of living units			150								150		150
Cash Paid plus Assumed Debt, excluding closing costs			22,350
Assumption of mortgage notes payable			12,266
Premium on Assumed Debt			1,040
Intangible assets recorded related to acquisition			1,039								1,039		1,039
Acquisition | Triple Net Leased Net Senior Living Communities | Stellar Senior Living, LLC
Real Estate Properties
Annual lease rent payable																			1,732
Acquisition | Managed Senior Living Communities
Real Estate Properties
Number of properties acquired or agreed to be acquired		2	5				1
Number of living units		228	374			228	93		228		374		374
Cash Paid plus Assumed Debt, excluding closing costs		47,430	62,999				22,030
Intangible assets recorded related to acquisition		3,119	4,075			3,119	1,013		3,119		4,075		4,075
Acquisition | MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired		2	6
Number of buildings acquired		3	7
Cash Paid plus Assumed Debt, excluding closing costs		1,156,963	117,475
Assumption of mortgage notes payable		15,630
Area of real estate properties (in square feet)		1,776,000	385,171,000			1,776,000			1,776,000		385,171,000		385,171,000
Premium on Assumed Debt		1,013
Intangible lease assets recorded		411,021	10,012			411,021			411,021		10,012		10,012
Intangible lease liabilities recorded		118,495	2,271			118,495			118,495		2,271		2,271
Acquisition | MOBs | Subsequent event
Real Estate Properties
Number of properties acquired or agreed to be acquired		23										23
Cash Paid plus Assumed Debt, excluding closing costs												539,000
Assumption of mortgage notes payable												30,000
Area of real estate properties (in square feet)												2,200,000
Acquisition | Senior living communities
Real Estate Properties
Number of properties acquired or agreed to be acquired		2	6
Sale
Real Estate Properties
Number of properties to be sold										6			3
Sale price of property sold and agreed to be sold										15,650			92,550
Gain on the sale of property										5,452			37,392
Sale | MOBs
Real Estate Properties
Number of properties to be sold		3												3
Number of buildings sold														3
Sale price of property sold and agreed to be sold														11,675
Gain on the sale of property														0
Sale | Senior living communities
Real Estate Properties
Number of properties to be sold		6
Sale | Senior living communities | Five Star
Real Estate Properties
Number of living units							112									156
Number of properties to be sold																2
Sale price of property sold and agreed to be sold							2,550									4,500
Increase or decrease in annual lease rent payable															285	(452)	210
Sale | Senior living communities | Five Star | Subsequent event
Real Estate Properties
Number of living units																		120
Sale price of property sold and agreed to be sold																		250
Increase or decrease in annual lease rent payable																		(23)
Sale | Skilled nursing facilities
Real Estate Properties
Number of properties to be sold													1
Sale | Rehabilitation hospitals
Real Estate Properties
Number of properties to be sold			2										2
Gain on the sale of property			36,251
Properties acquired in 2014
Real Estate Properties
Intangible lease assets recorded		414,140				414,140			414,140
Intangible lease liabilities recorded		118,495				118,495			118,495
Properties acquired in 2013
Real Estate Properties
Intangible lease assets recorded			17,131								17,131		17,131
Intangible lease liabilities recorded			2,271								2,271		2,271
Agreement to acquire | Senior living communities
Real Estate Properties
Number of communities						38
Number of living units		3,466				3,466			3,466
Number of states in which property is located		16				16			16
Cash Paid plus Assumed Debt, excluding closing costs						790,000
Assumption of mortgage notes payable						153,000
Weighted average interest rate on debt (as a percent)						4.80%
Agreement to acquire | Senior living communities | Leasing Member
Real Estate Properties
Number of communities						18
Number of living units		1,847				1,847			1,847
Number of operators						6
Number of operators currently tenants of the entity						0
Agreement to acquire | Senior living communities | Non Leasing Member
Real Estate Properties
Number of communities						20
Number of living units		1,619				1,619			1,619
Number of operators						6
Number of operators currently property managers under the entity						0
Number of leasing managers in group of non leasing operators						1
Land
Real Estate Properties
Real estate properties, at cost		683,979	623,756			683,979			683,979		623,756		623,756
Land | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Property plant and equipment recorded			5,120
Land | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded		2,803	5,155				1,548
Land | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded		55,784	13,899
Buildings and improvements
Real Estate Properties
Real estate properties, at cost		5,318,178	4,423,517			5,318,178			5,318,178		4,423,517		4,423,517
Accumulated depreciation		848,605	723,258			848,605			848,605		723,258		723,258
Buildings and improvements | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Property plant and equipment recorded			16,562
Buildings and improvements | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded		40,819	52,155				18,666
Buildings and improvements | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded		809,666	95,835
Furniture, fixtures and equipment
Real Estate Properties
Real estate properties, at cost		236,454	216,352			236,454			236,454		216,352		216,352
Accumulated depreciation		135,245	117,502			135,245			135,245		117,502		117,502
Furniture, fixtures and equipment | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Property plant and equipment recorded			669
Furniture, fixtures and equipment | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded		689	1,614				803
WA | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Number of properties acquired or agreed to be acquired																			1
Number of living units																			150
Cash Paid plus Assumed Debt, excluding closing costs																			22,350
Assumption of mortgage notes payable																			12,266
Premium on Assumed Debt																			1,040
Intangible assets recorded related to acquisition																			1,039
WA | Acquisition | MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired																				1
Cash Paid plus Assumed Debt, excluding closing costs																				38,000
Area of real estate properties (in square feet)																				145,000
Intangible lease assets recorded																				6,736
Intangible lease liabilities recorded																				1,588
WA | Land | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Property plant and equipment recorded																			5,120
WA | Land | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded																				5,639
WA | Buildings and improvements | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Property plant and equipment recorded																			16,562
WA | Buildings and improvements | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded																				27,213
WA | Furniture, fixtures and equipment | Acquisition | Triple Net Leased Net Senior Living Communities
Real Estate Properties
Property plant and equipment recorded																			669
MA | Acquisition | MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired							1														1
Cash Paid plus Assumed Debt, excluding closing costs							49,500														1,124,031
Area of real estate properties (in square feet)							105,000														1,651,000
Intangible lease assets recorded																					403,349
Intangible lease liabilities recorded																					118,485
MA | Land | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded							4,559														52,643
MA | Buildings and improvements | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded							44,941														786,524
Texas | Acquisition | MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired																						1
Cash Paid plus Assumed Debt, excluding closing costs																						32,932
Assumption of mortgage notes payable																						15,630
Area of real estate properties (in square feet)																						125,000
Premium on Assumed Debt																						1,013
Intangible lease assets recorded																						7,672
Intangible lease liabilities recorded																						10
Texas | Sale | Senior living communities | Five Star
Real Estate Properties
Number of living units																	36
Sale price of property sold and agreed to be sold																	2,400
Texas | Land | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded																						3,141
Texas | Buildings and improvements | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded																						23,142
Virginia | Sale | Senior living communities | Five Star
Real Estate Properties
Number of living units										70					70
Sale price of property sold and agreed to be sold															2,850
Arizona | Sale | Senior living communities | Five Star
Real Estate Properties
Number of living units										177					177
Number of properties to be sold															2
Sale price of property sold and agreed to be sold															5,900
Increase or decrease in annual lease rent payable															(590)
Various | Acquisition | Managed Senior Living Communities
Real Estate Properties
Number of properties acquired or agreed to be acquired																							3
Number of living units																							213
Cash Paid plus Assumed Debt, excluding closing costs																							29,004
Intangible assets recorded related to acquisition																							2,289
Various | Land | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded																							2,242
Various | Buildings and improvements | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded																							23,861
Various | Furniture, fixtures and equipment | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded																							612
WI | Acquisition | Managed Senior Living Communities
Real Estate Properties
Number of properties acquired or agreed to be acquired						1																		1
Number of living units		52				52			52															68
Cash Paid plus Assumed Debt, excluding closing costs						7,000																		11,965
Intangible assets recorded related to acquisition		849				849			849															773
WI | Additional acquisition | Managed Senior Living Communities
Real Estate Properties
Number of properties acquired or agreed to be acquired						1
Number of living units		176				176			176
Cash Paid plus Assumed Debt, excluding closing costs						40,430
Intangible assets recorded related to acquisition		2,270				2,270			2,270
WI | Land | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded						188																		1,365
WI | Land | Additional acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded						2,615
WI | Buildings and improvements | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded						5,862																		9,628
WI | Buildings and improvements | Additional acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded						34,957
WI | Furniture, fixtures and equipment | Acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded						101																		199
WI | Furniture, fixtures and equipment | Additional acquisition | Managed Senior Living Communities
Real Estate Properties
Property plant and equipment recorded						588
PENNSYLVANIA | Senior living communities | Subsequent event
Real Estate Properties
Number of properties to be sold																		1
Sale price of property sold and agreed to be sold																		250
MS | Acquisition | MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired																									1
Cash Paid plus Assumed Debt, excluding closing costs																									14,600
Area of real estate properties (in square feet)																									72,000
Intangible lease assets recorded																									1,498
Intangible lease liabilities recorded																									683
MS | Land | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded																									1,269
MS | Buildings and improvements | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded																									12,516
FL | Acquisition | MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired											3
Cash Paid plus Assumed Debt, excluding closing costs											15,375
Area of real estate properties (in square feet)			63,000								63,000		63,000
Intangible lease assets recorded			1,778								1,778		1,778
FL | Land | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded											2,432
FL | Buildings and improvements | Acquisition | MOBs
Real Estate Properties
Property plant and equipment recorded											11,165