Discontinued Operations and Dispositions of Real Estate - 2016 Dispositions (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) property	Jan. 31, 2017 USD ($) facility	Dec. 31, 2017 property facility	Dec. 31, 2016 USD ($) facility	Dec. 31, 2015 USD ($) facility
Post-acute/skilled | Disposed of by Sale | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility				5
Senior housing triple-net | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed	64		4	7	9
Total consideration for disposition of real estate | $	$ 1,125,000			$ 88,000	$ 60,000
Senior housing triple-net | Disposed of by Sale | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility				2
Post-acute/skilled and SH NNN | Disposed of by Sale | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration for disposition of real estate | $				$ 130,000
Life science
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility		4
Total consideration for disposition of real estate | $		$ 76,000
Life science | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility				5
Total consideration for disposition of real estate | $				$ 386,000	$ 51,000
Life science | Disposed of by Sale | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property			1,000
Medical office | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility			4	3	1
Total consideration for disposition of real estate | $				$ 20,000	$ 400
SHOP | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility			5	3
Total consideration for disposition of real estate | $				$ 41,000