DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Summary of the Notional Amount and Fair Value of Derivatives) (Details) - USD ($)		12 Months Ended
	Jan. 19, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 21, 2018	Sep. 18, 2018	May 17, 2018	Jun. 12, 2017
Fair value of derivative instruments
Total fair value derivative assets		$ 346,000	$ 4,470,000
Total fair value derivative liabilities		(16,517,000)	(5,961,000)
Repayment of debt		838,462,000	1,350,226,000	$ 333,302,000
Aggregate principal amount of debt issued								$ 200,000,000
Interest Rate Cap | Not Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 5.0 Maturing August 2019
Fair value of derivative instruments
Notional Amount		$ 75,000,000
Fixed interest rate		5.00%
Total fair value derivative assets		$ 0	0
Interest Rate Cap | Not Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 2.50%, Maturing December 2019
Fair value of derivative instruments
Notional Amount		$ 230,000,000
Fixed interest rate		2.50%
Total fair value derivative assets		$ 333,000	164,000
Interest income		(200,000)
Interest rate swap contracts | Designated as Hedging Instrument
Fair value of derivative instruments
Notional Amount		250,000,000					$ 250,000,000
Interest rate swap contracts | Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 1.66%, Maturing May 2020
Fair value of derivative instruments
Notional Amount		$ 40,000,000			$ 40,000,000
Fixed interest rate		1.66%
Total fair value derivative assets		$ 0	299,000
Interest rate swap contracts | Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 1.14%, Maturing September 2021
Fair value of derivative instruments
Notional Amount		$ 119,359,000			$ 119,400,000
Fixed interest rate		1.14%
Total fair value derivative assets		$ 0	4,007,000
Interest rate swap contracts | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.96%, Maturing October 2019
Fair value of derivative instruments
Notional Amount		$ 18,926,000
Fixed interest rate		2.96%
Total fair value derivative liabilities		$ 0	(286,000)
Interest rate swap contracts | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.65%, Maturing December 2027
Fair value of derivative instruments
Notional Amount		$ 50,000,000
Fixed interest rate		2.65%
Total fair value derivative liabilities		$ 0	(1,124,000)
Interest rate swap contracts | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.68%, Maturing December 2027
Fair value of derivative instruments
Notional Amount		$ 100,000,000
Fixed interest rate		2.68%
Total fair value derivative liabilities		$ 0	(2,509,000)
Interest rate swap contracts | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.62%, Maturing December 2027
Fair value of derivative instruments
Notional Amount		$ 100,000,000
Fixed interest rate		2.62%
Total fair value derivative liabilities		$ 0	(2,042,000)
Interest rate swap contracts | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.96 Maturing September 2023
Fair value of derivative instruments
Notional Amount		$ 615,000,000
Fixed interest rate		2.96%
Total fair value derivative liabilities		$ (13,781,000)	0
Interest Rate Collar | Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 1.50% To 2.50%, Maturing May 2019
Fair value of derivative instruments
Notional Amount		51,592,000
Total fair value derivative assets		13,000	0
Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.00% To 3.00%, Maturing May 2020
Fair value of derivative instruments
Notional Amount		193,967,000
Total fair value derivative liabilities		(37,000)	0
Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.25% To 3.25%, Maturing May 2021
Fair value of derivative instruments
Notional Amount		354,217,000
Total fair value derivative liabilities		(730,000)	0
Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.75% To 3.50%, Maturing April 2022
Fair value of derivative instruments
Notional Amount		381,404,000
Total fair value derivative liabilities		$ (1,969,000)	$ 0
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 1.50% To 2.50%, Maturing May 2019
Fair value of derivative instruments
Fixed interest rate		1.50%
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.00% To 3.00%, Maturing May 2020
Fair value of derivative instruments
Fixed interest rate		2.00%
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.25% To 3.25%, Maturing May 2021
Fair value of derivative instruments
Fixed interest rate		2.25%
Minimum | Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.75% To 3.50%, Maturing April 2022
Fair value of derivative instruments
Fixed interest rate		2.75%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets | Fixed Interest Rate 1.50% To 2.50%, Maturing May 2019
Fair value of derivative instruments
Fixed interest rate		2.50%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.00% To 3.00%, Maturing May 2020
Fair value of derivative instruments
Fixed interest rate		3.00%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.25% To 3.25%, Maturing May 2021
Fair value of derivative instruments
Fixed interest rate		3.25%
Maximum | Interest Rate Collar | Designated as Hedging Instrument | Accounts Payable and Accrued Liabilities | Fixed Interest Rate 2.75% To 3.50%, Maturing April 2022
Fair value of derivative instruments
Fixed interest rate		3.50%
110 N Wacker
Fair value of derivative instruments
Total fair value derivative liabilities	$ (300,000)
Repayment of debt	$ 18,900,000
$700 Million Loan Maturity September 2023
Fair value of derivative instruments
Fixed interest rate					4.61%
Aggregate principal amount of debt issued						$ 700,000,000.0
Term Loan | $700 Million Loan Maturity September 2023
Fair value of derivative instruments
Aggregate principal amount of debt issued						$ 615,000,000.0