DISPOSITIONS - Real Estate Assets Held For Sale (Details) $ in Thousands	Mar. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	1,200
Assets held for sale	$ 59,860	$ 9,608
Liabilities related to assets held for sale	3,853	3,246
Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	0	4,960
Liabilities related to assets held for sale	0	2,690
Office Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	55,416	15
Liabilities related to assets held for sale	3,352	101
Senior Living Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	4,444	4,633
Liabilities related to assets held for sale	$ 501	$ 455
Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	14	2
Disposal Group, Held-for-sale, Not Discontinued Operations | Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	0	1
Disposal Group, Held-for-sale, Not Discontinued Operations | Office Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	13	0
Disposal Group, Held-for-sale, Not Discontinued Operations | Senior Living Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	1	1