Real Estate and Accumulated Depreciation (Schedule III Real Estate and Accumulated Depreciation) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		$ 2,616,125
Initial Cost of Land		2,653,655
Initial Cost of Buildings & Improvements		26,257,700
Cost Capitalized Subsequent to Acquisition		1,956,105
Carrying Amount of Land		2,734,467
Carrying Amount of Buildings and Improvements		27,847,481
Accumulated Depreciation		4,838,370	$ 4,093,494	$ 3,796,297	$ 3,020,908
Investments In Real Property Owned Continuing Operations [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		2,550,443
Initial Cost of Land		2,653,655
Initial Cost of Buildings & Improvements		26,257,700
Cost Capitalized Subsequent to Acquisition		1,956,105
Carrying Amount of Land		2,734,467
Carrying Amount of Buildings and Improvements		27,847,481
Accumulated Depreciation	[1]	4,838,370
Triple Net [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		343,361
Initial Cost of Land		818,863
Initial Cost of Buildings & Improvements		7,759,508
Cost Capitalized Subsequent to Acquisition		382,344
Carrying Amount of Land		847,780
Carrying Amount of Buildings and Improvements		8,112,937
Accumulated Depreciation	[1]	1,380,023
Seniors Housing Operating [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		1,988,700
Initial Cost of Land		1,174,980
Initial Cost of Buildings & Improvements		12,626,419
Cost Capitalized Subsequent to Acquisition		1,234,180
Carrying Amount of Land		1,246,991
Carrying Amount of Buildings and Improvements		13,788,584
Accumulated Depreciation	[1]	2,362,335
Outpatient Medical [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		218,382
Initial Cost of Land		574,346
Initial Cost of Buildings & Improvements		4,724,190
Cost Capitalized Subsequent to Acquisition		315,225
Carrying Amount of Land		639,696
Carrying Amount of Buildings and Improvements		4,974,067
Accumulated Depreciation	[1]	1,096,012
Construction in Progress [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		0
Initial Cost of Land		0
Initial Cost of Buildings & Improvements		237,746
Cost Capitalized Subsequent to Acquisition		0
Carrying Amount of Land		0
Carrying Amount of Buildings and Improvements		237,746
Accumulated Depreciation	[1]	0
Assets Held-for-sale [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Encumbrances		65,682
Initial Cost of Land		85,466
Initial Cost of Buildings & Improvements		909,837
Cost Capitalized Subsequent to Acquisition		24,356
Carrying Amount of Land		0
Carrying Amount of Buildings and Improvements		734,147
Accumulated Depreciation	[1]	$ 0

[1] Please see Note 2 to our consolidated financial statements for information regarding lives used for depreciation and amortization.