FAIR VALUE DISCLOSURES - Face Values, Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Financial assets:
Loans receivable	$ 68,486,000	$ 96,492,000
Preferred equity investments	44,005,000	43,851,000
Senior Notes
Financial liabilities:
Financial liabilities	1,100,000,000	1,300,000,000
Secured Indebtedness
Financial liabilities:
Financial liabilities	115,370,000	117,464,000
Carrying Amount
Financial assets:
Loans receivable	63,825,000	69,460,000
Preferred equity investments	44,417,000	44,262,000
Carrying Amount | Senior Notes
Financial liabilities:
Financial liabilities	1,106,484,000	1,307,394,000
Carrying Amount | Secured Indebtedness
Financial liabilities:
Financial liabilities	113,644,000	115,679,000
Fair Value
Financial assets:
Loans receivable	61,008,000	65,797,000
Preferred equity investments	44,753,000	43,825,000
Fair Value | Senior Notes
Financial liabilities:
Financial liabilities	1,166,203,000	1,270,877,000
Fair Value | Secured Indebtedness
Financial liabilities:
Financial liabilities	$ 110,579,000	$ 101,820,000