SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended		30 Months Ended
	Sep. 30, 2020 USD ($) variableInterestEntity investment	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2020 USD ($) variableInterestEntity investment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2020 USD ($)	Jan. 01, 2020 USD ($)	Jun. 30, 2019 USD ($)
Accounting Policies [Line Items]
Number of investments in loans accounted for as real estate joint ventures | investment	0			0
Net income	$ 36,460	$ 23,286		$ 101,300	$ 29,277
Income (loss) from unconsolidated joint venture	2,766	(605)		$ (13,037)	$ (5,635)
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Cumulative effect of ASU adoption	3,364,340	3,282,417	$ 3,361,251	$ 3,364,340	$ 3,282,417	$ 3,488,460	$ 3,254,747	$ 3,361,251		$ 3,260,376
Total assets	(5,991,618)			(5,991,618)		(6,069,299)
Resident Fee and Services Fee
Accounting Policies [Line Items]
Grant income	1,200			1,200
Loss from Unconsolidated Joint Venture
Accounting Policies [Line Items]
Grant income	3,000			3,000
Out of Period Adjustment | Correction of Depreciation and Amortization Expense
Accounting Policies [Line Items]
Net income			5,200			100	(1,700)	3,600
Income (loss) from unconsolidated joint venture			5,200			100	(1,700)	3,600
Cumulative Distributions in Excess of Net Income
Accounting Policies [Line Items]
Net income	36,460	23,282		101,300	29,255
Cumulative effect of ASU adoption	$ (689,828)	$ (523,709)	$ (663,901)	$ (689,828)	$ (523,709)	(573,283)	(271,595)	$ (663,901)		$ (460,832)
Primary Beneficiary
Accounting Policies [Line Items]
Number of variable interest entities | variableInterestEntity	0			0
Cumulative Effect in Period of Adoption
Accounting Policies [Line Items]
Cumulative effect of ASU adoption						(167)	(32,502)
Total assets									$ 200
Cumulative Effect in Period of Adoption | Cumulative Distributions in Excess of Net Income
Accounting Policies [Line Items]
Cumulative effect of ASU adoption						$ (167)	$ (32,502)		$ 200