INVESTMENT IN UNCONSOLIDATED JOINT VENTURES (110 William Street Refinancing) (Details)	Mar. 07, 2019 USD ($) extension	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Face amount		$ 382,126,000	$ 403,802,000
Interest Rate Cap
Schedule of Equity Method Investments [Line Items]
Notional amount	$ 348,500,000
One-month LIBOR | Interest Rate Cap
Schedule of Equity Method Investments [Line Items]
Reference rate	3.75%
110 William Joint Venture | 110 William Street Mortgage Loan
Schedule of Equity Method Investments [Line Items]
Extinguishment of debt	$ 268,000,000
Face amount	$ 261,400,000.0
Number of extensions | extension	3
Extension period	1 year
Contractual interest rate, percentage	3.50%
110 William Joint Venture | Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Face amount	$ 87,100,000.0
Contractual interest rate, percentage	6.90%
Amount outstanding	$ 70,300,000
110 William Joint Venture | Senior Mortgage Loan
Schedule of Equity Method Investments [Line Items]
Extinguishment of debt	215,500,000
Amount outstanding	210,800,000
Unused borrowing capacity, amount	4,700,000
110 William Joint Venture | Building Loan
Schedule of Equity Method Investments [Line Items]
Extinguishment of debt	45,900,000
Unused borrowing capacity, amount	45,900,000
110 William Joint Venture | 110 William Street Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Unused borrowing capacity, amount	$ 16,800,000
110 William Joint Venture | One-month LIBOR | 110 William Street Mortgage Loan
Schedule of Equity Method Investments [Line Items]
Basis spread on variable rate	1.50%
110 William Joint Venture | One-month LIBOR | Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Basis spread on variable rate	4.90%