Dispositions and Impairments - 2019 Dispositions Activity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property senior_housing	Dec. 31, 2018 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	1,200
Gain on real estate dispositions | $	$ 262,218	$ 26,022	$ 46,247
2019 Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Vacant Land Parcels Sold | senior_housing		1
Proceeds from sale of real estate | $		$ 147,500
Gain on real estate dispositions | $		$ 26,000
Triple-net leased properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	366
Triple-net leased properties | 2019 Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties		10
Medical Office Buildings | 2019 Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties		8
Seniors Housing Communities | 2019 Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties		6