SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)		12 Months Ended
	Jan. 02, 2018 USD ($) Property director	Dec. 31, 2019 USD ($) Property variable_interest_entity Segment Investment	Dec. 31, 2018 USD ($) Investment	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Number of investments in loans accounted for as real estate joint ventures | Investment		0	0
Acquisition costs capitalized		$ 600,000	$ 700,000
Merger and acquisition costs		$ 424,000	636,000	$ 30,255,000
Extension period for tenant relationship intangible assets		10 years
Assets held for sale		$ 0	0
Book value of investment in the joint venture		319,460,000	340,120,000
Restricted cash		$ 10,046,000	9,428,000
Number of reportable segments | Segment		1
Operating lease liability		$ 9,800,000
Operating lease right-of-use asset		9,300,000
ASU 2016-02
Property, Plant and Equipment [Line Items]
Operating lease liability					$ 10,000,000.0
Operating lease right-of-use asset					10,000,000
Cumulative effect of Topic 842 adoption					32,502,000
Straight-line rent receivable					17,500,000
Cash rent receivable					$ 15,000,000.0
Variable lease, income		17,600,000
Restricted Cash Obligations
Property, Plant and Equipment [Line Items]
Restricted cash		5,600,000	5,500,000
Skilled Nursing/Transitional Care
Property, Plant and Equipment [Line Items]
Net investment in direct financing lease		$ 23,900,000
Properties in direct financing lease | Property		1
Undiscounted rental payments		$ 4,000,000.0
Estimated unguaranteed residual value		24,700,000
Unearned lease income		4,800,000
Income from direct financing lease		2,700,000
Income from direct financing lease			$ 2,600,000	$ 1,000,000.0
Future minimum lease payments contractually due under direct financing lease, 2020		2,300,000
Future minimum lease payments contractually due under direct financing lease, 2021		$ 2,100,000
Land Improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets		5 years
Land Improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets		20 years
Buildings and Building Improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets		5 years
Buildings and Building Improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets		40 years
Furniture and Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets		3 years
Furniture and Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets		20 years
Enlivant Joint Venture
Property, Plant and Equipment [Line Items]
Number of real estate properties acquired | Property	172
Enlivant Joint Venture | Senior Housing Facilities
Property, Plant and Equipment [Line Items]
Number of properties sold | Property		2
Proceeds from sale of real estate		$ 6,300,000
Enlivant Joint Venture
Property, Plant and Equipment [Line Items]
Payments to acquire equity interest, before closing costs	$ 352,700,000
Equity interest acquired	49.00%
Outstanding indebtedness	$ 791,300,000
Net working capital	$ 22,900,000
Number of directors appointed by minority interest | director	3
Total number of directors | director	7
Gain (loss) on sale of properties		(1,700,000)
Book value of investment in the joint venture		$ 319,500,000
Primary Beneficiary
Property, Plant and Equipment [Line Items]
Number of variable interest entities | variable_interest_entity		0