Real Estate Transactions - Held for Sale (Details) $ in Thousands	1 Months Ended				3 Months Ended								12 Months Ended
	Jan. 31, 2020 USD ($) property	Oct. 31, 2019 property	Mar. 31, 2017 facility	Jan. 31, 2017 facility	Dec. 31, 2019 USD ($) property	Sep. 30, 2019 USD ($) property	Jun. 30, 2019 USD ($) property	Mar. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property facility	Sep. 30, 2018 facility	Jun. 30, 2018 facility	Mar. 31, 2018 facility	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net					$ 504,394				$ 108,086				$ 504,394	$ 108,086
Accumulated depreciation and amortization					$ 2,771,922				$ 2,842,947				2,771,922	2,842,947
Proceeds from sale of buildings													$ 0	$ 335,709	$ 462,242
Senior housing triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility			64								2				4
Number of assets to be sold (in properties) | property								2
Medical office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility										2					4
Number of assets to be sold (in properties) | property					4	1	5						4
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility									2	11	8	2			5
Number of assets to be sold (in properties) | property					7	1	1	9					7
Life science
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | facility				4						4					1
Number of assets to be sold (in properties) | property							1	1
Held-for-sale | Senior housing triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale | property					27								27
Held-for-sale | Medical office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale | property					2								2
Held-for-sale | SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale | property					28				9				28	9
Held-for-sale | Senior Housing Triple-Net and SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net					$ 504,000								$ 504,000
Held-for-sale | Life science
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale | property									1					1
Held-for-sale | SH NNN, Life Science, SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net									$ 108,000					$ 108,000
Real estate | Held-for-sale | Senior Housing Triple-Net and SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net					476,000								476,000
Other liabilities					4,000								4,000
Debt on assets held for sale					32,000								32,000
Accumulated depreciation and amortization					243,000								$ 243,000
Real estate | Held-for-sale | SH NNN, Life Science, SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net									101,000					101,000
Accumulated depreciation and amortization									$ 30,000					$ 30,000
Brookedale MTCA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property		18
Subsequent Event | SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold (in properties) | property	6
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings					$ 92,000	$ 7,000	$ 14,000	$ 68,000
SHOP | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings	$ 36,000