DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - AOCI (Details)			12 Months Ended
	Nov. 29, 2017 USD ($) swap	Aug. 03, 2017 USD ($) swap	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES
Balance, at beginning of period			$ 966,589,000	$ 1,297,347,000	$ 1,359,816,000
Balance, at end of period			626,705,000	966,589,000	1,297,347,000
Number of swaps terminated | swap	4	3
Notional amount of terminated swaps	$ 150,000,000	$ 65,000,000
Amounts reclassified to interest expense upon interest rate hedge termination	926,000		8,000
Payment of derivative fees and accrued interest			38,000
Proceeds from termination payments, net of fees			1,011,000
Unsecured term facility entered into in May 2015
DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES
Repayments of debt	$ 150,000,000	$ 65,000,000
Changes related to interest rate swaps designated as cash flow hedges
DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES
Balance, at beginning of period			(509,000)	(2,519,000)	0
Other comprehensive income (loss) before reclassifications			361,000	(2,227,000)	(3,381,000)
Amounts reclassified from accumulated other comprehensive income (loss)			1,779,000	4,237,000	862,000
Net current period other comprehensive income (loss)			2,140,000	2,010,000	(2,519,000)
Balance, at end of period			1,631,000	$ (509,000)	$ (2,519,000)
Cash flow hedges
DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES
Amount of gain (loss) expected to be reclassified from AOCI to earnings during the next twelve months			$ 8,000