DISPOSITIONS - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Aug. 31, 2017 USD ($) property	Dec. 31, 2017 USD ($) property	Sep. 30, 2017 USD ($) property parcel	Sep. 30, 2016 USD ($)	Dec. 31, 2016 property	Nov. 30, 2016 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Vacant parcels sold | parcel			3
Proceeds from sale of real estate			$ 617.1
Gain on sale of real estate			$ 502.3
Number of Properties Classified as Held-for-sale | property			22		7
Impairment of real estate			$ 20.2	$ 14.5
Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties sold | property			37
Medical Office Buildings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties sold | property			3
Skilled Nursing Facilities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties sold | property	22
Proceeds from sale of real estate	$ 488.1
Gain on sale of real estate	$ 458.0
Potential properties for sale under agreement | property						36
Kindred
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Potential proceeds from sale of property under agreement						$ 700.0
Scenario, Forecast | Subsequent Event | Skilled Nursing Facilities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties sold | property		7
Proceeds from sale of real estate		$ 82.5
Potential gain on sale of real estate		$ 78.0
Number of Properties Classified as Held-for-sale | property		7