DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Summary of the Notional Amount and Fair Value of Derivatives) (Details)		3 Months Ended	9 Months Ended		12 Months Ended
	Jan. 19, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) settled_derivative termination_event	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) termination_event	Sep. 21, 2018 USD ($)	Sep. 18, 2018 USD ($)	May 17, 2018 USD ($)
Fair value of derivative instruments
Termination events | termination_event			4		0
Gain on unwinding of swaps			$ 16,104,000	$ 0
Total fair value derivative assets					$ 4,470,000
Total fair value derivative liabilities		$ (1,749,000)	(1,749,000)		(5,961,000)
Interest rate swap derivative assets		1,288,000	1,288,000		4,470,000
Repayments on mortgage loan			656,816,000	$ 1,130,337,000
Interest rate swaps
Fair value of derivative instruments
Loss on missed forecast and amortization of terminated swaps		200,000	$ 500,000
Interest rate swap agreements settled | settled_derivative			3
Interest rate swaps | Designated as Hedging Instrument
Fair value of derivative instruments
Notional		$ 250,000,000.0	$ 250,000,000.0					$ 250,000,000
Gain on unwinding of swaps			16,100,000
Derivative change in fair value recognition period		9 years 6 months
Gain on derivative expected amount to be reclassified		$ 1,400,000	1,400,000
Interest rate swaps | Designated as Hedging Instrument | Accounts payable and accrued expenses | Fixed Interest Rate 2.96%, Maturing October 2019
Fair value of derivative instruments
Notional		$ 18,926,000	$ 18,926,000
Fixed Interest Rate		2.96%	2.96%
Total fair value derivative liabilities		$ 0	$ 0		(286,000)
Interest rate swaps | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 1.66%, Maturing May 2020
Fair value of derivative instruments
Notional						$ 40,000,000
Derivative change in fair value recognition period			1 year 7 months 6 days
Fixed Interest Rate		1.66%	1.66%
Total fair value derivative assets		$ 0	$ 0		299,000
Interest rate swaps | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 1.14%, Maturing September 2021
Fair value of derivative instruments
Notional						$ 119,359,000
Derivative change in fair value recognition period			3 years
Fixed Interest Rate		1.14%	1.14%
Total fair value derivative assets		$ 0	$ 0		4,007,000
Interest rate swaps | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.65%, Maturing December 2027
Fair value of derivative instruments
Notional		$ 50,000,000	$ 50,000,000
Fixed Interest Rate		2.65%	2.65%
Total fair value derivative liabilities		$ 0	$ 0		(1,124,000)
Interest rate swaps | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.68%, Maturing December 2027
Fair value of derivative instruments
Notional		$ 100,000,000	$ 100,000,000
Fixed Interest Rate		2.68%	2.68%
Total fair value derivative liabilities		$ 0	$ 0		(2,509,000)
Interest rate swaps | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.62%, Maturing December 2027
Fair value of derivative instruments
Notional		$ 100,000,000	$ 100,000,000
Fixed Interest Rate		2.62%	2.62%
Total fair value derivative liabilities		$ 0	$ 0		(2,042,000)
Interest rate swaps | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.96%, Maturing September 2023
Fair value of derivative instruments
Notional		$ 615,000	$ 615,000
Fixed Interest Rate		2.96%	2.96%
Total fair value derivative liabilities		$ (1,355,000)	$ (1,355,000)		0
Interest Rate Cap | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate5.00 Maturing August2019
Fair value of derivative instruments
Notional		$ 75,000,000	$ 75,000,000
Fixed Interest Rate		5.00%	5.00%
Total fair value derivative assets		$ 0	$ 0		0
Interest Rate Cap | Not Designated as Hedging Instrument, Economic Hedge | Accounts payable and accrued expenses | Fixed Interest Rate 2.50%, Maturing December 2019
Fair value of derivative instruments
Interest (income) expense		100,000	600,000
Interest Rate Cap | Not Designated as Hedging Instrument, Economic Hedge | Prepaid expenses and other assets, net | Fixed Interest Rate 2.50%, Maturing December 2019
Fair value of derivative instruments
Notional		$ 230,000,000	$ 230,000,000
Fixed Interest Rate		2.50%	2.50%
Total fair value derivative assets		$ 751,000	$ 751,000		164,000
Interest Rate Collar | Designated as Hedging Instrument | Accounts payable and accrued expenses | Fixed Interest Rate 2.75% To 3.50%, Maturing April 2022
Fair value of derivative instruments
Notional		381,404,000	381,404,000
Total fair value derivative liabilities		(394,000)	(394,000)		0
Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 1.50% To 2.50%, Maturing May 2019
Fair value of derivative instruments
Notional		51,592,000	51,592,000
Total fair value derivative assets		26,000	26,000		0
Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.00% To 3.00%, Maturing May 2020
Fair value of derivative instruments
Notional		193,967,000	193,967,000
Total fair value derivative assets		168,000	168,000		0
Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.25% To 3.25%, Maturing May 2021
Fair value of derivative instruments
Notional		354,217,000	354,217,000
Total fair value derivative assets		$ 343,000	$ 343,000		$ 0
Wacker110 N
Fair value of derivative instruments
Total fair value derivative liabilities	$ (300,000)
Repayments on mortgage loan	$ 18,900,000
Minimum | Interest rate swaps | Designated as Hedging Instrument | Accounts payable and accrued expenses | Fixed Interest Rate 2.75% To 3.50%, Maturing April 2022
Fair value of derivative instruments
Fixed Interest Rate		2.75%	2.75%
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 1.50% To 2.50%, Maturing May 2019
Fair value of derivative instruments
Fixed Interest Rate		1.50%	1.50%
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.00% To 3.00%, Maturing May 2020
Fair value of derivative instruments
Fixed Interest Rate		2.00%	2.00%
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.25% To 3.25%, Maturing May 2021
Fair value of derivative instruments
Fixed Interest Rate		2.25%	2.25%
Maximum | Interest rate swaps | Designated as Hedging Instrument | Accounts payable and accrued expenses | Fixed Interest Rate 2.75% To 3.50%, Maturing April 2022
Fair value of derivative instruments
Fixed Interest Rate		3.50%	3.50%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 1.50% To 2.50%, Maturing May 2019
Fair value of derivative instruments
Fixed Interest Rate		2.50%	2.50%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.00% To 3.00%, Maturing May 2020
Fair value of derivative instruments
Fixed Interest Rate		3.00%	3.00%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid expenses and other assets, net | Fixed Interest Rate 2.25% To 3.25%, Maturing May 2021
Fair value of derivative instruments
Fixed Interest Rate		3.25%	3.25%
$700 Million Loan Maturity September 2023
Fair value of derivative instruments
Fixed Interest Rate						4.61%
Loan amount							$ 700,000,000.0
Term Loan | $700 Million Loan Maturity September 2023
Fair value of derivative instruments
Loan amount							$ 615,000,000