Real Property Acquisitions and Development (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Unsecured debt		$ (8,331,722)		$ (8,161,619)
Seniors Housing Operating [Member]
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Land and land improvements		42,525		164,653		$ 218,581
Buildings and improvements		428,777		1,518,472		2,367,486
Acquired lease intangibles		63,912		115,643		187,512
Receivables and other assets		3,959		2,462		29,501
Total assets acquired	[1]	539,173		1,801,230		2,803,080
Secured debt		0		(63,732)		(871,471)
Unsecured debt		0		0		(24,621)
Accrued expenses and other liabilities		(46,301)		(23,681)		(81,778)
Total liabilities assumed		(46,301)		(87,413)		(977,870)
Noncontrolling interests		(4,701)		(6,007)		(183,854)
Non-cash acquisition related activity		(67,633)	[2]	(47,065)	[3]	0
Cash disbursed for acquisitions		420,538		1,660,745		1,641,356
Construction in progress additions		84,874		157,845		44,173
Less: Capitalized interest		(9,106)		(5,793)		(1,740)
Less: Foreign currency translation		(6,830)		(8,500)		(2,499)
Cash disbursed for construction in progress		68,938		143,552		39,934
Capital improvements to existing properties		185,473		138,673		104,308
Total cash invested in real property, net of cash acquired		674,949		1,942,970		1,785,598
Cash acquired from acquisition		6,273		351		42,728
Non cash acquisition financed as real estate loan receivable		6,349
Non cash acquisition financed as equity investments		59,665		43,372
Triple Net [Member]
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Land and land improvements		33,416		104,754		95,835
Buildings and improvements		248,459		418,633		1,061,431
Acquired lease intangibles		0		2,876		4,408
Receivables and other assets		0		551		194
Total assets acquired	[4]	281,875		526,814		1,161,868
Secured debt		0		0		(47,741)
Accrued expenses and other liabilities		(21,236)		(3,384)		(2,905)
Total liabilities assumed		(21,236)		(3,384)		(50,646)
Noncontrolling interests		(7,275)		(26,771)		(13,465)
Non-cash acquisition related activity		(54,901)		(51,733)		(38,355)
Cash disbursed for acquisitions		198,463		444,926		1,059,402
Construction in progress additions		120,797		181,084		143,140
Less: Capitalized interest		(4,713)		(8,729)		(5,699)
Less: Foreign currency translation		(610)		(3,665)		(167)
Cash disbursed for construction in progress		115,474		168,690		137,274
Capital improvements to existing properties		19,989		32,603		45,293
Total cash invested in real property, net of cash acquired		333,926		646,219		1,241,969
Cash acquired from acquisition		318		682		16,578
Non cash acquisition financed as real estate loan receivable	[5]	54,901		45,044		23,288
Non cash acquisition financed as equity investments				6,630		6,743
Outpatient Medical [Member]
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Land and land improvements		40,565		5,738		223,708
Buildings and improvements		159,643		46,056		614,770
Acquired lease intangibles		24,014		4,592		45,226
Receivables and other assets		10		0		939
Total assets acquired		224,232		56,386		884,643
Secured debt		(25,708)		0		(120,977)
Accrued expenses and other liabilities		(3,181)		(1,670)		(7,777)
Total liabilities assumed		(28,889)		(1,670)		(128,754)
Noncontrolling interests		(9,080)		0		(76,535)
Non-cash acquisition related activity		0		(15,013)	[6]	(27,025)	[7]
Cash disbursed for acquisitions	[8]	186,263		39,703		652,329
Construction in progress additions		37,094		113,933		70,560
Less: Capitalized interest		(2,406)		(3,723)		(1,286)
Accruals	[9]	13,615		(19,321)		(1,921)
Cash disbursed for construction in progress		48,303		90,889		67,353
Capital improvements to existing properties		44,814		47,870		38,151
Total cash invested in real property, net of cash acquired		$ 279,380		$ 178,462		757,833
Cash acquired from acquisition						$ 5,522

[1] Excludes $6,273,000, $351,000 and $42,728,000 of cash and restricted cash acquired during the years ended December 31, 2017, 2016 and 2015, respectively.

[2] Includes $59,665,000 related to the acquisition of assets previously financed as investments in unconsolidated entities, and $6,349,000 related to the acquisition of assets previously financed as real estate loans receivable.

[3] Includes $43,372,000 related to the acquisition of assets previously financed as investments in unconsolidated entities.

[4] Excludes $318,000, $682,000 and $16,578,000 of cash and restricted cash acquired during the years ended December 31, 2017, 2016 and 2015, respectively.

[5] For the year ended December 31, 2017, $54,901,000 is related to the acquisition of assets previously financed as real estate loans receivable. For the year ended December 31, 2016, primarily relates to $45,044,000 for the acquisition of assets previously financed as real estate loans receivable and $6,630,000 previously financed as an equity investment. For the year ended December 31, 2015, primarily relates to $23,288,000 for the acquisition of assets previously financed as real estate loans receivable and $6,743,000 previously financed as equity investments.

[6] The non-cash activity relates to the acquisition of assets previously financed as real estate loans. Please refer to Note 6 for additional information.

[7] The non-cash activity relates to the acquisition of a controlling interest in a portfolio of properties that was historically reported as an unconsolidated property investment.

[8] Excludes $5,522,000 of cash acquired during the year ended December 31, 2015.

[9] Represents non-cash consideration accruals for amounts to be paid in future periods for properties that converted, off-set by amounts paid in the current period.