Schedule III - Real Estate and Accumulated Depreciation (Summary) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	$ 2,485,711
Initial Cost of Land	3,141,623
Initial Cost of Buildings & Improvements	28,882,284
Cost Capitalized Subsequent to Acquisition	1,868,125
Carrying Amount of Land	3,205,091
Carrying Amount of Buildings and Improvements	30,385,297
Accumulated Depreciation	5,499,958	$ 4,838,370	$ 4,093,494	$ 3,796,297
Triple-net
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	288,387
Initial Cost of Land	1,096,169
Initial Cost of Buildings & Improvements	8,585,481
Cost Capitalized Subsequent to Acquisition	301,960
Carrying Amount of Land	1,119,576
Carrying Amount of Buildings and Improvements	8,864,034
Accumulated Depreciation	1,261,486
Seniors Housing Operating
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	1,810,587
Initial Cost of Land	1,331,171
Initial Cost of Buildings & Improvements	14,047,033
Cost Capitalized Subsequent to Acquisition	1,206,757
Carrying Amount of Land	1,373,258
Carrying Amount of Buildings and Improvements	15,211,900
Accumulated Depreciation	2,962,334
Outpatient Medical
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	386,737
Initial Cost of Land	645,891
Initial Cost of Buildings & Improvements	5,233,682
Cost Capitalized Subsequent to Acquisition	357,411
Carrying Amount of Land	712,257
Carrying Amount of Buildings and Improvements	5,524,727
Accumulated Depreciation	1,276,138
Construction in Progress [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	0
Initial Cost of Land	0
Initial Cost of Buildings & Improvements	194,365
Cost Capitalized Subsequent to Acquisition	0
Carrying Amount of Land	0
Carrying Amount of Buildings and Improvements	194,365
Accumulated Depreciation	0
Investments In Real Property Owned Continuing Operations [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	2,485,711
Initial Cost of Land	3,073,231
Initial Cost of Buildings & Improvements	28,060,561
Cost Capitalized Subsequent to Acquisition	1,866,128
Carrying Amount of Land	3,205,091
Carrying Amount of Buildings and Improvements	29,795,026
Accumulated Depreciation	5,499,958
Assets Held-for-sale [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances	0
Initial Cost of Land	68,392
Initial Cost of Buildings & Improvements	821,723
Cost Capitalized Subsequent to Acquisition	1,997
Carrying Amount of Land	0
Carrying Amount of Buildings and Improvements	590,271
Accumulated Depreciation	$ 0