REAL ESTATE PROPERTIES HELD FOR INVESTMENT - Narrative (Details)			1 Months Ended			3 Months Ended	4 Months Ended	9 Months Ended	10 Months Ended	12 Months Ended
	Apr. 01, 2019 USD ($) facility	Dec. 19, 2018 facility	Jan. 31, 2020 facility	May 31, 2019 facility	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) facility	Jan. 31, 2020 facility	Dec. 31, 2019 USD ($) facility	Jan. 31, 2020 facility	Dec. 31, 2019 USD ($) facility	Dec. 31, 2018 USD ($) facility	Dec. 31, 2017 USD ($)
Real Estate Properties [Line Items]
Weighted average expiration period						8 years		8 years		8 years
Security deposit liability						$ 10,500,000		$ 10,500,000		$ 10,500,000	$ 12,400,000
Letters of credit deposited						83,000,000		83,000,000		83,000,000	98,000,000
Deposits held for future real estate taxes, insurance expenditures and tenant improvement						$ 14,300,000		$ 14,300,000		14,300,000	17,500,000
Reserve for unpaid cash rents											1,300,000
Reserve associated with straight-line rental income											35,800,000
Portion of settlement applied to post-petition rent										6,200,000
Impairment of real estate										121,819,000	1,413,000	$ 1,326,000
Gain (loss) on termination of lease										10,579,000	0	0
Resident fees and services										128,058,000	70,137,000	26,430,000
Ancillary Services
Real Estate Properties [Line Items]
Resident fees and services										$ 800,000	500,000	$ 300,000
Minimum
Real Estate Properties [Line Items]
Operating lease expiration period						1 year		1 year		1 year
Maximum
Real Estate Properties [Line Items]
Operating lease expiration period						15 years		15 years		15 years
Holiday Retirement
Real Estate Properties [Line Items]
Lease termination, income	$ 66,900,000
Total consideration received upon termination	57,200,000
Gain (loss) on termination of lease	$ 9,700,000
2019 Dispositions
Real Estate Properties [Line Items]
Impairment of real estate										$ 95,200,000
Senior Care Centers Sale Facilities
Real Estate Properties [Line Items]
Impairment of real state, related to indemnity										10,200,000
Contractual indemnification obligation						$ 8,800,000		$ 8,800,000		$ 8,800,000
Senior Care Centers
Real Estate Properties [Line Items]
Litigation settlement, amount awarded from other party					$ 9,500,000
Senior Care Centers | 2019 Dispositions | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties [Line Items]
Number of properties sold | facility	28
Senior Care Centers | 2019 Dispositions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Subsequent Event
Real Estate Properties [Line Items]
Number of properties sold | facility									2
Senior Care Centers | Senior Care Centers Sale Facilities
Real Estate Properties [Line Items]
Aggregate sales price	$ 282,500,000
Senior Housing - Managed
Real Estate Properties [Line Items]
Senior housing communities subject to the master lease | facility		21
Skilled Nursing/Transitional Care | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties [Line Items]
Impairment of real estate											$ 900,000
Skilled Nursing/Transitional Care | 2019 Dispositions | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties [Line Items]
Number of properties sold | facility								5		39
Skilled Nursing/Transitional Care | Senior Care Centers Sale Facilities
Real Estate Properties [Line Items]
Number of properties sold | facility	26					1
Number of real estate properties transitioned | facility				8
Skilled Nursing/Transitional Care | Senior Care Centers Sale Facilities | Subsequent Event
Real Estate Properties [Line Items]
Number of properties sold | facility			1				2
Senior Housing Communities | 2019 Dispositions | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties [Line Items]
Number of properties sold | facility										7
Senior Housing Communities | Senior Care Centers Sale Facilities
Real Estate Properties [Line Items]
Number of properties sold | facility	2
Operating Segments
Real Estate Properties [Line Items]
Number of properties | facility						429		429		429	470
Operating Segments | Senior Housing - Managed
Real Estate Properties [Line Items]
Number of properties | facility						46		46		46	23