DISPOSITIONS - DISPOSITIONS - (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) property parcel	Sep. 30, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Vacant parcels sold | parcel	2
Proceeds from real estate disposals | $	$ 326,100
Net gain on the sale of assets, net of tax | $	35,900
Impairment of real estate | $	$ 10,700	$ 20,200
Medical Office Buildings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of real estate properties sold | property	9
Senior Living Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of real estate properties sold | property	7
Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of real estate properties sold | property	5