Real Property Acquisitions and Development (Summary of Real Property Investment Activity) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Real property held for sale	$ 590,271,000	$ 734,147,000
Seniors Housing Operating
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Land and land improvements	51,440,000	42,525,000	$ 164,653,000
Buildings and improvements	621,731,000	428,777,000	1,518,472,000
Acquired lease intangibles	69,504,000	63,912,000	115,643,000
Receivables and other assets	1,492,000	3,959,000	2,462,000
Total assets acquired	744,167,000	539,173,000	1,801,230,000
Secured debt	(134,752,000)	0	(63,732,000)
Accrued expenses and other liabilities	(18,463,000)	(46,301,000)	(23,681,000)
Total liabilities assumed	(153,215,000)	(46,301,000)	(87,413,000)
Noncontrolling interests	(14,390,000)	(4,701,000)	(6,007,000)
Non-cash acquisition related activity	0	(67,633,000)	(47,065,000)
Cash disbursed for acquisitions	576,562,000	420,538,000	1,660,745,000
Construction in progress additions	82,621,000	84,874,000	157,845,000
Capitalized interest	(3,190,000)	(9,106,000)	(5,793,000)
Foreign currency translation	3,934,000	(6,830,000)	(8,500,000)
Cash disbursed for construction in progress	83,365,000	68,938,000	143,552,000
Capital improvements to existing properties	201,001,000	185,473,000	138,673,000
Total cash invested in real property, net of cash acquired	860,928,000	674,949,000	1,942,970,000
Cash acquired from acquisition	5,784,000	6,273,000	351,000
Non cash acquisition financed as equity investments		59,665,000	43,372,000
Non cash acquisition financed as real estate loan receivable		6,349,000
Triple-net
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Land and land improvements	413,588,000	33,416,000	104,754,000
Buildings and improvements	2,242,884,000	248,459,000	418,633,000
Acquired lease intangibles	9,690,000	0	2,876,000
Real property held for sale	396,265,000	0	0
Receivables and other assets	1,354,000	0	551,000
Total assets acquired	3,063,781,000	281,875,000	526,814,000
Accrued expenses and other liabilities	(13,199,000)	(21,236,000)	(3,384,000)
Total liabilities assumed	(13,199,000)	(21,236,000)	(3,384,000)
Noncontrolling interests	(512,741,000)	(7,275,000)	(26,771,000)
Non-cash acquisition related activity	0	(54,901,000)	(51,733,000)
Cash disbursed for acquisitions	2,537,841,000	198,463,000	444,926,000
Construction in progress additions	55,558,000	120,797,000	181,084,000
Capitalized interest	(2,238,000)	(4,713,000)	(8,729,000)
Foreign currency translation	272,000	(610,000)	(3,665,000)
Cash disbursed for construction in progress	53,592,000	115,474,000	168,690,000
Capital improvements to existing properties	10,046,000	19,989,000	32,603,000
Total cash invested in real property, net of cash acquired	2,601,479,000	333,926,000	646,219,000
Cash acquired from acquisition	386,894,000	318,000	682,000
Non cash acquisition financed as equity investments			6,630,000
Non cash acquisition financed as real estate loan receivable		54,901,000	45,044,000
Outpatient Medical
Estimated Fair Value of Allocated Purchase Price of Asset and Liabilities
Land and land improvements	77,239,000	40,565,000	5,738,000
Buildings and improvements	478,740,000	159,643,000	46,056,000
Acquired lease intangibles	50,813,000	24,014,000	4,592,000
Real property held for sale	22,032,000	0	0
Receivables and other assets	1,185,000	10,000	0
Total assets acquired	630,009,000	224,232,000	56,386,000
Secured debt	(169,156,000)	(25,708,000)	0
Accrued expenses and other liabilities	(14,896,000)	(3,181,000)	(1,670,000)
Total liabilities assumed	(184,052,000)	(28,889,000)	(1,670,000)
Noncontrolling interests	0	(9,080,000)	0
Non-cash acquisition related activity	0	0	(15,013,000)
Cash disbursed for acquisitions	445,957,000	186,263,000	39,703,000
Construction in progress additions	26,565,000	37,094,000	113,933,000
Capitalized interest	(2,477,000)	(2,406,000)	(3,723,000)
Accruals	(339,000)	13,615,000	(19,321,000)
Cash disbursed for construction in progress	23,749,000	48,303,000	90,889,000
Capital improvements to existing properties	55,136,000	44,814,000	47,870,000
Total cash invested in real property, net of cash acquired	524,842,000	$ 279,380,000	$ 178,462,000
Cash acquired from acquisition	$ 2,719,000