REAL ESTATE AND RELATED LEASE INTANGIBLES, NET - Real Estate Properties Sold (Details)		1 Months Ended	12 Months Ended
		Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 67,104,000	$ 12,123,000	$ 157,008,000
Net Book Value	[1]		985,304,000	1,048,081,000
Realized gain (loss) on sale of real estate, net		$ 0	32,102,000	1,392,000	95,881,000
2020 Disposal Properties
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			98,738,000
Net Book Value			66,636,000
Realized gain (loss) on sale of real estate, net			32,102,000
2020 Disposal Properties | Condominium | Miami, FL
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			1,832,000
Net Book Value			1,821,000
Realized gain (loss) on sale of real estate, net			$ 11,000
Properties | property			0
Units Sold | property			6
Units Remaining | property			0
2020 Disposal Properties | Diversified | Richmond, VA
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 22,527,000
Net Book Value			14,829,000
Realized gain (loss) on sale of real estate, net			$ 7,698,000
Properties | property			7
Units Sold | property			0
Units Remaining | property			0
2020 Disposal Properties | Diversified | Richmond, VA
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 6,932,000
Net Book Value			4,109,000
Realized gain (loss) on sale of real estate, net			$ 2,823,000
Properties | property			1
Units Sold | property			0
Units Remaining | property			0
2020 Disposal Properties | Diversified | Lithia Springs, GA
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 39,491,000
Net Book Value			23,187,000
Realized gain (loss) on sale of real estate, net			$ 16,304,000
Properties | property			1
Units Sold | property			0
Units Remaining | property			0
2020 Disposal Properties | Diversified | Winston Salem, North Carolina
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 4,647,000
Net Book Value			3,803,000
Realized gain (loss) on sale of real estate, net			$ 844,000
Properties | property			1
Units Sold | property			0
Units Remaining | property			0
2020 Disposal Properties | Diversified | South Bend, IN
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 3,875,000
Net Book Value			3,875,000
Realized gain (loss) on sale of real estate, net			$ 0
Properties | property			1
Units Sold | property			0
Units Remaining | property			0
2020 Disposal Properties | Net Lease | Bellport, NY
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds			$ 19,434,000
Net Book Value			15,012,000
Realized gain (loss) on sale of real estate, net			$ 4,422,000
Properties | property			1
Units Sold | property			0
Units Remaining | property			0
2019 Disposal Properties
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds				24,242,000
Net Book Value				22,670,000
Realized gain (loss) on sale of real estate, net				1,572,000
2019 Disposal Properties | Condominium | Miami, FL
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds				4,715,000
Net Book Value				4,282,000
Realized gain (loss) on sale of real estate, net				$ 433,000
Properties | property				0
Units Sold | property				16
Units Remaining | property				6
2019 Disposal Properties | Condominium | Las Vegas, NV
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds				$ 809,000
Net Book Value				415,000
Realized gain (loss) on sale of real estate, net				$ 394,000
Properties | property				0
Units Sold | property				1
Units Remaining | property				0
2019 Disposal Properties | Diversified | Wayne, NJ
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds				$ 1,729,000
Net Book Value				4,799,000
Realized gain (loss) on sale of real estate, net				$ (3,070,000)
Properties | property				1
Units Sold | property				0
Units Remaining | property				0
2019 Disposal Properties | Diversified | Grand Rapids, Michigan
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds				$ 10,019,000
Net Book Value				8,254,000
Realized gain (loss) on sale of real estate, net				$ 1,765,000
Properties | property				1
Units Sold | property				0
Units Remaining | property				0
2019 Disposal Properties | Diversified | Grand Rapids, Michigan 1
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds				$ 6,970,000
Net Book Value				4,920,000
Realized gain (loss) on sale of real estate, net				$ 2,050,000
Properties | property				1
Units Sold | property				0
Units Remaining | property				0
2018 Disposal Properties
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds					218,662,000
Net Book Value					122,781,000
Realized gain (loss) on sale of real estate, net					95,881,000
Realized Gain Allocated to Third Party Investor					15,316,000
2018 Disposal Properties | Condominium | Miami, FL
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds					7,851,000
Net Book Value					6,716,000
Realized gain (loss) on sale of real estate, net					1,135,000
Realized Gain Allocated to Third Party Investor					$ 0
Properties | property					0
Units Sold | property					26
Units Remaining | property					22
2018 Disposal Properties | Condominium | Las Vegas, NV
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds					$ 8,763,000
Net Book Value					4,458,000
Realized gain (loss) on sale of real estate, net					4,305,000
Realized Gain Allocated to Third Party Investor					$ 0
Properties | property					0
Units Sold | property					12
Units Remaining | property					1
2018 Disposal Properties | Diversified | Richmond, VA
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds					$ 20,966,000
Net Book Value					11,370,000
Realized gain (loss) on sale of real estate, net					9,596,000
Realized Gain Allocated to Third Party Investor					$ 389,000
Properties | property					1
Units Sold | property					0
Units Remaining | property					0
2018 Disposal Properties | Diversified | El Monte, CA
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds					$ 71,807,000
Net Book Value					52,610,000
Realized gain (loss) on sale of real estate, net					19,197,000
Realized Gain Allocated to Third Party Investor					$ 6,999,000
Properties | property					1
Units Sold | property					0
Units Remaining | property					0
2018 Disposal Properties | Diversified | St. Paul, MN
Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds					$ 109,275,000
Net Book Value					47,627,000
Realized gain (loss) on sale of real estate, net					61,648,000
Realized Gain Allocated to Third Party Investor					$ 7,928,000
Properties | property					4
Units Sold | property					0
Units Remaining | property					0

[1] Includes amounts relating to consolidated variable interest entities. See Note 1 and Note 10.