DISPOSITIONS - Real Estate Assets Held For Sale (Details) $ in Thousands	Sep. 30, 2019 USD ($) property	Dec. 31, 2018 USD ($) 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	$ 4,520	$ 5,454
Liabilities related to assets held for sale	1,531	205
Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	3,645	5,482
Liabilities related to assets held for sale	573	40
Office Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	8	160
Liabilities related to assets held for sale	403	152
Senior Living Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	867	(188)
Liabilities related to assets held for sale	$ 555	$ 13
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	3	1
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	2	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	0	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	0