FAIR VALUE DISCLOSURES - Face Values, Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Financial assets:
Loans receivable	$ 64,692,000	$ 65,320,000
Preferred equity investments	44,634,000	43,724,000
Senior Notes
Financial liabilities:
Financial liabilities	1,250,000,000	1,250,000,000
Secured Indebtedness
Financial liabilities:
Financial liabilities	79,682,000	80,199,000
Carrying Amount
Financial assets:
Loans receivable	56,364,000	58,899,000
Preferred equity investments	44,861,000	43,940,000
Carrying Amount | Senior Notes
Financial liabilities:
Financial liabilities	1,248,464,000	1,248,393,000
Carrying Amount | Secured Indebtedness
Financial liabilities:
Financial liabilities	78,562,000	79,065,000
Fair Value
Financial assets:
Loans receivable	57,045,000	60,421,000
Preferred equity investments	45,487,000	44,597,000
Fair Value | Senior Notes
Financial liabilities:
Financial liabilities	1,357,113,000	1,362,678,000
Fair Value | Secured Indebtedness
Financial liabilities:
Financial liabilities	$ 76,052,000	$ 79,326,000