DISPOSITIONS - DISPOSITIONS - (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) property parcel	Sep. 30, 2018 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	1,200		1,200
Proceeds from sale of real estate | $			$ 77,300
Gain on real estate dispositions | $	$ 36	$ 18	24,633	$ 35,893
Impairment of real estate | $			$ 22,600	$ 10,700
Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	423		423
2019 Dispositions
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Vacant land parcels sold | parcel			1
2019 Dispositions | Triple-Net Leased Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	8		8
2019 Dispositions | Medical Office Buildings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	8		8
2019 Dispositions | Seniors Housing Communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	1		1