Segment Disclosures - Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Segment Disclosure
Assets held for sale, net		$ 9,819
Total assets	21,369,940	20,075,870
Goodwill	50,346	50,346
Impairment related to goodwill	0
Operating segment
Segment Disclosure
Gross assets	23,042,397	21,381,636
Accumulated depreciation and amortization	(2,600,072)	(2,257,188)
Total assets	20,442,325	19,124,448
Operating segment | Senior housing
Segment Disclosure
Gross assets	8,383,345	7,803,085
Goodwill	31,000
Operating segment | Post-acute/skilled
Segment Disclosure
Gross assets	6,875,122	6,266,938
Goodwill	3,000
Operating segment | Life science
Segment Disclosure
Gross assets	4,154,789	3,986,187
Operating segment | Medical office
Segment Disclosure
Gross assets	2,988,888	2,686,069
Goodwill	11,000
Operating segment | Hospital
Segment Disclosure
Gross assets	640,253	639,357
Goodwill	5,000
Other non-segment
Segment Disclosure
Total assets	$ 927,615	$ 941,603