FAIR VALUE DISCLOSURES - Face Values, Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial Assets [Abstract]
Loans receivable	$ 76,212	$ 91,280
Preferred equity investments	49,782	48,035
Senior Notes
Financial Liabilities Fair Value Disclosure [Abstract]
Senior Notes	1,300,000	1,300,000
Secured Indebtedness
Financial Liabilities Fair Value Disclosure [Abstract]
Senior Notes	257,660	259,202
Carrying Amount
Financial Assets [Abstract]
Loans receivable	50,640	65,907
Preferred equity investments	50,248	48,483
Carrying Amount | Senior Notes
Financial Liabilities Fair Value Disclosure [Abstract]
Secured indebtedness	1,306,566	1,306,286
Carrying Amount | Secured Indebtedness
Financial Liabilities Fair Value Disclosure [Abstract]
Secured indebtedness	254,917	256,430
Fair Value
Financial Assets [Abstract]
Loans receivable	52,516	65,892
Preferred equity investments	47,846	47,064
Fair Value | Senior Notes
Financial Liabilities Fair Value Disclosure [Abstract]
Secured indebtedness	1,299,303	1,329,191
Fair Value | Secured Indebtedness
Financial Liabilities Fair Value Disclosure [Abstract]
Secured indebtedness	$ 237,903	$ 246,461