INVESTMENT IN REAL ESTATE PROPERTIES - Net Investment in Direct Financing Lease (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Real Estate [Line Items]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Cumulative effect of ASU adoption	$ 3,364,340	$ 3,282,417	$ 3,364,340	$ 3,282,417	$ 3,361,251		$ 3,488,460	$ 3,260,376	$ 3,254,747
Direct Financing Lease, Income, Comprehensive Income [Extensible List]		us-gaap:InterestAndFeeIncomeLoansAndLeases		us-gaap:InterestAndFeeIncomeLoansAndLeases
Skilled Nursing Transitional Care Facilities
Real Estate [Line Items]
Net investment in direct financing lease	$ 24,100		$ 24,100
Number of properties in direct financing lease | property	1		1
Undiscounted rental payments	$ 2,800		$ 2,800
Estimated purchase price	24,800		24,800
Unearned lease income	3,300		3,300
Allowance for credit losses related to direct financing lease	200		200
Lease income	700	$ 700	2,000	$ 2,000
Reduction in the allowance for credit losses related to direct financing lease	1		38
Future minimum lease payments contractually due under the direct financing lease for the remainder of this year	600		600
Future minimum lease payments contractually due under the direct financing lease due for next year	2,300		2,300
Future minimum lease payments contractually due under the direct financing lease due for year two	$ 100		$ 100
Cumulative Effect in Period of Adoption
Real Estate [Line Items]
Cumulative effect of ASU adoption							$ (167)		$ (32,502)
Cumulative Effect in Period of Adoption | Skilled Nursing Transitional Care Facilities | Direct Financing Lease
Real Estate [Line Items]
Cumulative effect of ASU adoption						$ (200)