Impairments (Details) $ / item in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / item property	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) property
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments (recoveries), net		$ 225,937	$ 55,260	$ 166,384
Number of real estate properties impaired | property		3
Asset impairment charge		$ 18,000
Casualty-Related
Casualty-related loss				13,000
Property damage loss in a casualty				8,000
Other associated costs with casualty loss				5,000
Deferred tax benefit related to casualty loss				1,000
Senior Housing Triple Net, SHOP, MOB, and Other Non-Reportable
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments (recoveries), net		$ 194,000
SHOP
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments (recoveries), net	$ 10,000		$ 52,000
Number of real estate properties impaired | property		27	17
Number Of real estate properties impaired, candidates for potential sale | property		1
Casualty-Related
Impairment of real estate		$ 5,000
SHOP | Underperformed assets
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property			3
Senior housing triple-net
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments (recoveries), net				$ 23,000
Number of real estate properties impaired | property		8		11
Medical office
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments (recoveries), net		$ 4,000
Number of real estate properties impaired | property		3
Number of properties intended to be demolished | property		1
Number Of real estate properties impaired, candidates for potential sale | property		2
Other non-reportable segments
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property		1
Other nonoperating income (expense)
Casualty-Related
Casualty-related loss				$ 12,000
Equity income (loss) from unconsolidated joint ventures
Casualty-Related
Casualty-related loss				$ 1,000
Held-for-sale | Life science
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property			1
Held-for-sale | SHOP
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property		28	9
Held-for-sale | Senior housing triple-net
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property		27
Held-for-sale | Medical office
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property		2
Land | Held-for-sale | Life science
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property			1
Seven Shop Assets, Four Senior Housing Triple-net Assets, Two MOBs, and One Other Non-Reportable Asset
Impaired Long-Lived Assets Held and Used [Line Items]
Aggregate carrying value before impairment		$ 416,000
Real estate held-for-sale		$ 223,000
Minimum
Impaired Long-Lived Assets Held and Used [Line Items]
Market capitalization rate		4.97%
Price per unit (in dollars per share) | $ / item		24
Maximum
Impaired Long-Lived Assets Held and Used [Line Items]
Market capitalization rate		8.27%
Price per unit (in dollars per share) | $ / item		125
Weighted Average
Impaired Long-Lived Assets Held and Used [Line Items]
Market capitalization rate		6.22%
Price per unit (in dollars per share) | $ / item		73