FAIR VALUE DISCLOSURES - Face Values, Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Loans receivable	$ 72,728,000	$ 96,492,000
Preferred equity investments	43,915,000	43,851,000
Senior Notes
Financial liabilities:
Financial liabilities	1,100,000,000	1,300,000,000
Secured Indebtedness
Financial liabilities:
Financial liabilities	116,421,000	117,464,000
Carrying Amount
Financial assets:
Loans receivable	66,876,000	69,460,000
Preferred equity investments	44,327,000	44,262,000
Carrying Amount | Senior Notes
Financial liabilities:
Financial liabilities	1,106,518,000	1,307,394,000
Carrying Amount | Secured Indebtedness
Financial liabilities:
Financial liabilities	114,675,000	115,679,000
Fair Value
Financial assets:
Loans receivable	63,977,000	65,797,000
Preferred equity investments	44,280,000	43,825,000
Fair Value | Senior Notes
Financial liabilities:
Financial liabilities	1,143,537,000	1,270,877,000
Fair Value | Secured Indebtedness
Financial liabilities:
Financial liabilities	$ 108,446,000	$ 101,820,000