SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)		12 Months Ended
	Jan. 02, 2018 USD ($) Property director	Dec. 31, 2018 USD ($) Property variable_interest_entity Segment Investment	Dec. 31, 2017 USD ($) Investment	Dec. 31, 2016 USD ($)	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		$ 700,000	$ 1,000,000
Merger and acquisition costs		$ 636,000	30,255,000	$ 1,197,000
Extension period for tenant relationship intangible assets		10 years
Assets held for sale		$ 0	0
Book value of investment in the joint venture		340,120,000	0
Restricted cash		$ 9,428,000	68,817,000
Restricted cash held by exchange accommodation titleholder			57,500,000
Number of reportable segments | Segment		1
Subsequent Event | Forecast
Property, Plant and Equipment [Line Items]
Operating lease liability					$ 10,000,000
Operating lease right-of-use asset					$ 10,000,000
Accumulated Other Comprehensive (Loss) Income
Property, Plant and Equipment [Line Items]
Cumulative effect of ASU 2017-12 adoption			795,000
ASU 2017-12 | Accumulated Other Comprehensive (Loss) Income
Property, Plant and Equipment [Line Items]
Cumulative effect of ASU 2017-12 adoption			800,000
Restricted Cash Obligations
Property, Plant and Equipment [Line Items]
Restricted cash		$ 5,500,000	6,500,000
Skilled Nursing/Transitional Care
Property, Plant and Equipment [Line Items]
Net investment in direct financing lease		$ 23,400,000
Properties in direct financing lease | Property		1
Undiscounted rental payments		$ 5,600,000
Estimated unguaranteed residual value		24,700,000
Unearned lease income		6,900,000
Income from direct financing lease		2,600,000	$ 1,000,000
Future minimum lease payments contractually due under direct financing lease, 2019		2,200,000
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		7 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
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
Book value of investment in the joint venture		$ 340,100,000
Primary Beneficiary
Property, Plant and Equipment [Line Items]
Number of variable interest entities | variable_interest_entity		1
Primary Beneficiary | Skilled Nursing/Transitional Care
Property, Plant and Equipment [Line Items]
Number of variable interest entities | variable_interest_entity		1