FAIR VALUE DISCLOSURES - Face Values, Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Financial assets:
Loans receivable	$ 66,316,000	$ 67,527,000
Preferred equity investments	42,533,000	43,893,000
Senior Notes
Financial liabilities:
Financial liabilities	1,250,000,000	1,250,000,000
Secured Indebtedness
Financial liabilities:
Financial liabilities	80,124,000	114,777,000
Carrying Amount
Financial assets:
Loans receivable	61,076,000	63,070,000
Preferred equity investments	42,744,000	44,304,000
Carrying Amount | Senior Notes
Financial liabilities:
Financial liabilities	1,248,324,000	1,248,773,000
Carrying Amount | Secured Indebtedness
Financial liabilities:
Financial liabilities	78,975,000	113,070,000
Fair Value
Financial assets:
Loans receivable	56,956,000	59,832,000
Preferred equity investments	43,039,000	44,493,000
Fair Value | Senior Notes
Financial liabilities:
Financial liabilities	1,311,354,000	1,328,714,000
Fair Value | Secured Indebtedness
Financial liabilities:
Financial liabilities	$ 79,249,000	$ 105,510,000