DISPOSITIONS - Real Estate Assets Held For Sale (Details) $ in Thousands	Mar. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) 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	$ 75,039	$ 91,433
Liabilities related to assets held for sale	5,007	5,463
Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	52,115	62,098
Liabilities related to assets held for sale	1,512	1,623
Office Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	1,496	5,177
Liabilities related to assets held for sale	1,397	499
Senior Living Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	21,428	24,158
Liabilities related to assets held for sale	$ 2,098	$ 3,341
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	13	15
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	8	8
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	0	1
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	5	6
Dispositions [Member] | Medical Office Buildings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	1
Dispositions [Member] | Senior Housing Communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | property	1