Acquisitions of Real Estate Property (Details) $ / shares in Units, CAD in Millions		1 Months Ended				3 Months Ended								12 Months Ended
	Aug. 04, 2015 USD ($) property	Sep. 30, 2016 USD ($) property	Aug. 31, 2015 property	Jan. 31, 2015 USD ($) property $ / shares shares	Aug. 31, 2014 CAD property	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) property	Dec. 31, 2015 USD ($) property	Dec. 31, 2014 USD ($) property shares	Feb. 29, 2016 USD ($)	Jul. 31, 2014 CAD	Aug. 31, 2004 CAD
Business Acquisition [Line Items]
Net real estate property						$ 20,394,754,000				$ 19,625,220,000				$ 20,394,754,000	$ 19,625,220,000
Revenues						875,713,000	$ 867,116,000	$ 848,404,000	$ 852,289,000	841,274,000	$ 827,606,000	$ 811,920,000	$ 805,598,000	3,443,522,000	3,286,398,000	$ 2,776,813,000
Business acquisition, transaction costs						$ 19,100,000				99,000,000				19,100,000	99,000,000	10,800,000
Amount paid for equity interest														$ 0	26,282,000	0
Ownership interests in properties accounted for under the equity method						5.00%								5.00%
Goodwill						$ 1,033,225,000				1,047,497,000				$ 1,033,225,000	1,047,497,000
Debt instrument, face amount																	$ 200,000,000
Merger-related expenses and deal costs														24,635,000	102,944,000	43,304,000
Unsecured Debt
Business Acquisition [Line Items]
Debt instrument, face amount										20,000,000					20,000,000
Triple-net leased properties
Business Acquisition [Line Items]
Goodwill						303,845,000								303,845,000
Senior Living Operations
Business Acquisition [Line Items]
Goodwill						259,482,000								259,482,000
Office Operations
Business Acquisition [Line Items]
Goodwill						469,898,000								469,898,000
Life Sciences Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses		$ 1,500,000,000
Life Sciences Acquisitions | Operating Property
Business Acquisition [Line Items]
Number of real estate properties acquired | property		23
Life Sciences Acquisitions | Development Assets
Business Acquisition [Line Items]
Number of real estate properties acquired | property		2
Life Sciences Acquisitions | Future Development Sites
Business Acquisition [Line Items]
Number of real estate properties acquired | property		9
Other 2016 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses														$ 0
Other 2016 Acquisitions | Medical Office Buildings
Business Acquisition [Line Items]
Number of real estate properties acquired | property														2
Other 2016 Acquisitions | Triple-net leased properties
Business Acquisition [Line Items]
Number of real estate properties acquired | property														1
Development Projects 2016
Business Acquisition [Line Items]
Net real estate property						31,900,000								$ 31,900,000
Development Projects 2016 | Medical Office Buildings
Business Acquisition [Line Items]
Number of real estate properties completed | property														2
Development Projects 2016 | Triple-net leased properties
Business Acquisition [Line Items]
Number of real estate properties completed | property														3
2016 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses														$ 1,428,944,000
Revenues														55,700,000
NOI														37,700,000
Business combination, notes payable and other debt assumed						47,641,000								47,641,000
2016 Acquisitions | Triple-net leased properties
Business Acquisition [Line Items]
Payments to acquire businesses														13,920,000
Business combination, notes payable and other debt assumed						0								0
2016 Acquisitions | Office Operations
Business Acquisition [Line Items]
Payments to acquire businesses														1,415,024,000
Business combination, notes payable and other debt assumed						$ 47,641,000								$ 47,641,000
American Realty Capital Healthcare Trust
Business Acquisition [Line Items]
Payments to acquire businesses				$ 11,000,000
Number of real estate properties acquired | property				152
Business combination, consideration transferred, stock conversion ratio, per acquiree share				0.1688
Business combination, consideration transferred, price per acquiree share (dollars per share) | $ / shares				$ 11.33
Business combination, notes payable and other debt assumed				$ 167,000,000
Business combination, repayment of debt				$ 730,000,000
American Realty Capital Healthcare Trust | Common Stock
Business Acquisition [Line Items]
Business acquisition, equity interest issued, number of shares | shares				28,400,000
American Realty Capital Healthcare Trust | Skilled Nursing Facilities
Business Acquisition [Line Items]
Number of real estate properties acquired | property			20
Ardent
Business Acquisition [Line Items]
Estimated fair value of investment	$ 1,300,000,000
Amount paid for equity interest	$ 26,300,000
Ownership interests in properties accounted for under the equity method	9.90%
Ardent | Triple-net leased properties
Business Acquisition [Line Items]
Number of real estate properties acquired | property	10
Other 2015 Acquisitions
Business Acquisition [Line Items]
Business combination, consideration transferred															$ 612,000,000
Other 2015 Acquisitions | Skilled Nursing Facilities
Business Acquisition [Line Items]
Number of real estate properties acquired | property															12
Other 2015 Acquisitions | Triple-net leased properties
Business Acquisition [Line Items]
Number of real estate properties acquired | property															11
Other 2015 Acquisitions | Office Operations
Business Acquisition [Line Items]
Number of real estate properties acquired | property															9
Other 2015 Acquisitions | Office Operations | Unconsolidated Properties
Business Acquisition [Line Items]
Number of real estate properties acquired | property															8
Development Projects 2015 | Triple-net leased properties
Business Acquisition [Line Items]
Net real estate property										9,300,000					$ 9,300,000
Development Projects 2015 | Triple-net leased properties | Seniors Housing Communities
Business Acquisition [Line Items]
Number of real estate properties completed | property															1
2015 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses															$ 2,685,981,000
Revenues															327,000,000
NOI															201,900,000
Business acquisition, transaction costs										4,100,000					4,100,000	1,400,000
Business combination, notes payable and other debt assumed										177,857,000					177,857,000
Goodwill										746,900,000					746,900,000
2015 Acquisitions | Triple-net leased properties
Business Acquisition [Line Items]
Business combination, notes payable and other debt assumed										0					0
Goodwill										133,600,000					133,600,000
2015 Acquisitions | Senior Living Operations
Business Acquisition [Line Items]
Business combination, notes payable and other debt assumed										77,940,000					77,940,000
Goodwill										219,100,000					219,100,000
2015 Acquisitions | Office Operations
Business Acquisition [Line Items]
Business combination, notes payable and other debt assumed										99,917,000					99,917,000
Goodwill										$ 394,200,000					$ 394,200,000
Limited Partnership Units | Common Stock
Business Acquisition [Line Items]
Business acquisition, equity interest issued, number of shares | shares				1,100,000
Holiday Retirement
Business Acquisition [Line Items]
Business combination, notes payable and other debt assumed | CAD																			CAD 193.7
Business combination, consideration transferred | CAD					CAD 957.0
Early debt repayment costs | CAD					CAD 26.9
Holiday Retirement | Unsecured Debt | Unsecured term loan due 2015
Business Acquisition [Line Items]
Debt instrument, face amount | CAD																		CAD 791.0
Holiday Retirement | Seniors Housing Communities
Business Acquisition [Line Items]
Number of real estate properties acquired | property					29
Other Acquisitions
Business Acquisition [Line Items]
Business combination, consideration transferred																812,000,000
Early debt repayment costs																$ 18,800,000
Other Acquisitions | Triple-net leased properties | Seniors Housing Communities
Business Acquisition [Line Items]
Number of real estate properties acquired | property																26
Other Acquisitions | Triple-net leased properties | Private Hospitals
Business Acquisition [Line Items]
Number of real estate properties acquired | property																3
Other Acquisitions | Senior Living Operations | Seniors Housing Communities
Business Acquisition [Line Items]
Number of real estate properties acquired | property																4
Other Acquisitions | Office Operations
Business Acquisition [Line Items]
Business acquisition, equity interest issued, number of shares | shares																148,241
Development Projects, 2014
Business Acquisition [Line Items]
Net real estate property																$ 41,200,000
Development Projects, 2014 | Seniors Housing Communities
Business Acquisition [Line Items]
Number of real estate properties completed | property																1
Development Projects, 2014 | Medical Office Buildings
Business Acquisition [Line Items]
Number of real estate properties completed | property																2
2014 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses																$ 1,469,217,000
Revenues																75,900,000
NOI																41,500,000
Business acquisition, transaction costs																26,200,000
Business combination, notes payable and other debt assumed																241,077,000
Merger-related expenses and deal costs																23,800,000
2014 Acquisitions | Triple-net leased properties
Business Acquisition [Line Items]
Payments to acquire businesses																599,782,000
Business combination, notes payable and other debt assumed																12,927,000
2014 Acquisitions | Senior Living Operations
Business Acquisition [Line Items]
Payments to acquire businesses																869,435,000
Business combination, notes payable and other debt assumed																$ 228,150,000